Please answer this math question.?

Question

Please answer this math question and give me the steps.

On a bookshelf, there are five different mystery books and six different biographies. How many different sets of four books can Emilio choose if two of the books must be mystery books and two of the books must be biographies?

Answer 1

she can choose 2 out of 5 mysteries
and independently choose 2 out of 6 biographies
the order of choosing the mysteries, and the biographies is not relevant

5C2 * 6C2 = 5 * 4 / 2 * 6 * 5 / 2 = 150

Answer 2

(5*4)*(6*5)=20*30=600