Both questions are substituting the letter (or pronumeral) for a number.
In the first question we swap the letter y for the number 1. This makes the question 5(3-4x1) . We complete the brackets first by multiplying 4 by 1 then subtract 3 from the answer. We then multiply our answer by 5 and there's you're final answer; -5.
The second question is only slightly more complicated in that there are two pronumerals to replace. We substitute the x for 5, 3(-5+4y) . Then we can substitute the y for -2 . The final question is 3(-5+4x-2) . To simplify we begin with the multiplication. 4x-2 is -8. 3(-5-8). Next we subtract -8 from -5 which equals -13. Multiply this by 3 to get the answer which is -39
