Which of the following accurately defines all possible values of p-q if 15≤p≤30 and 7≤q≤19?

Question

The answer is -4≤(p-q)≤23, but I'm not sure how.

Thank you!

Answer 1

p-q is largest if p is big and q is small:

p-q <= 30-7 = 23

similarly,

p-q >= 15-19 = -4