Mi tutora dice que trescientas palabras bastan para una reseña breve y clara.

Because palabras is a feminine plural noun, and the hundreds in Spanish agree in gender with the noun they modify.

• trescientas palabras
• trescientos libros

This only happens with the hundreds (doscientos/doscientas, trescientos/trescientas, etc.), not with smaller numbers like tres.

Because the subject is trescientas palabras, which is plural.

The verb bastar means to be enough or to suffice, so Spanish treats three hundred words as the thing that is enough.

• Una palabra basta = One word is enough
• Tres palabras bastan = Three words are enough

So in this sentence:

• trescientas palabras bastan = three hundred words are enough

Bastar works a bit differently from the English idea of need. It focuses on what is sufficient, not what is required.

So:

• Trescientas palabras bastan = Three hundred words are enough
• No bastan = They are not enough

It is very common in Spanish and sounds natural here. The sentence is not saying what the review needs in an absolute sense; it is saying that three hundred words are sufficient for that purpose.

Tutora is the feminine form of tutor.

Depending on context, especially in Spain, tutor/a can mean:

• a teacher responsible for a class group
• an academic adviser or mentor
• a supervisor for a project or dissertation
• sometimes a private tutor, depending on context

So mi tutora could mean my female tutor, my adviser, or my form tutor/class tutor, depending on the situation.

Because decir que is the normal way to introduce reported speech or a statement.

• Dice que... = He/She says that...
• Pienso que... = I think that...
• Cree que... = He/She believes that...

In English, that is often omitted:

• My tutor says three hundred words are enough...

But in Spanish, que is normally kept:

• Mi tutora dice que...

Because Spanish usually does not use an article before a number when you are simply stating a quantity.

• Cien personas vinieron
• Tres libros bastan
• Trescientas palabras bastan

If you added an article, it would usually change the meaning and make it more specific:

• Las trescientas palabras... = the three hundred words

That would refer to a particular set of words, not just the amount.

Here para means for, expressing purpose or suitability.

So:

• bastan para una reseña = are enough for a review

The rest describes the kind of review:

• breve = brief
• clara = clear

So the structure is:

• [quantity] + bastan + para + [purpose]

Examples:

• Cinco minutos bastan para explicarlo.
• Eso basta para empezar.

In Spanish, descriptive adjectives often come after the noun.

• una reseña breve
• una explicación clara
• un texto interesante

So una reseña breve y clara is the most neutral, standard order.

You can sometimes place adjectives before the noun, but that often adds emphasis or a more literary tone. Here, post-noun position is the natural everyday choice.

Because some Spanish adjectives have the same form for masculine and feminine, while others change.

• breve → same for both:

  • un texto breve
  • una reseña breve

• claro/clara → changes:

  • un texto claro
  • una reseña clara

Both adjectives still have to agree in number, though:

• reseñas breves y claras

Reseña often means review, especially of a book, film, play, or similar work. But it can also mean a short written overview or brief account, depending on context.

In many educational contexts, reseña is a short review-style text that summarises and comments on something.

So here it likely means something like:

• a short review
• a brief review piece
• possibly a short write-up, depending on the class context

Yes. Trescientas palabras son suficientes para una reseña breve y clara is also correct.

The difference is mainly style:

• bastan = more concise, a bit more direct
• son suficientes = slightly more explicit

Both are natural. Bastar is especially elegant here because it directly expresses the idea of sufficiency in one verb.

No. It should be mi, without an accent, because it is a possessive adjective meaning my.

Compare:

• mi tutora = my tutor
• mí = me, after a preposition
  
  • para mí
  • sin mí

So in this sentence, mi is correct because it modifies tutora.