Jill sold half of her comic books then bought 16 more, she now has 36. With how many did she begin with? Break it down please

A: 40

Let’s do this problem backwards.

TOTAL BOOKS RN: 36

1)
“Jill... then bought 16 more...”

36 - 16 = 20

After subtracting that amount, we would end up with half of the books Jill DID NOT sell.

2)
2 • 20 = 40

At this point, we multiplied amount of books she had after she sold half of her comic books by the reciprocal of 1/2

And now you have your answer!