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write the sentences margarita would say to indicate that she has completed each errand. use the appropriate direct object pronouns (lo, los, la, las).
modelo sacar un libro de la biblioteca lo saqué.
echar una carta

La eché

Explanation:

Echar una carta = Take a letter.

We first need to identify the appropriate direct object pronoun.  What's the subject of "Echar una carta"?  

The subject is "una carta", so it's feminine and singular, so the direct object pronoun to use is "la".

Now, we need to conjugate the verb "echar" to past time, for the first personal pronoun (yo)... that is "eché" since it's first group.

So, in total: La eché.