Don’t understand what your asking in the first one. Choosing a vowel out of the word counting would be 3/8. And picking a consonant out of the word prime would be 3/5.
the student has left 75 because if you add 5 and 70 it gives you $75 that's how much the student had left.
So you would just have to divide 20/7 to get the percentage of it.
The answer would be 2.85%.