"This is my problem."
Translation:Это моя проблема.
Why are some words that end in -a written with эта whereas others are written with это? I thought эта was feminine?
This problem is difficult - Эта проблема сложная
This is my problem - Это моя проблема
The difference is that in the second case 'this' is used as a subject (you could replace it with a noun), while in the first case it's used as an attribute (you could replace it with an adjective).
Also, not all words ending with а are feminine.
I'm not 100% on this, but I think it's plural, feminine, masculine, and neuter (respectively). Since Russian nouns have genders, (bread, хлеб is masculine while dog, собака is feminine, for example), the corresponding pronoun needs to have the same gender.
Maybe this translation isn't ideal for this exercise but "это моя дела" could have the same meaning right