Brittney can chop 15 / 5 = 3 onions in one minute. Carl can chop 20 / 5 = 4 onions in one minute. Brittney can chop 3 x 30 = 90 onions in 30 minutes. Carl can chop 4 x 30 = 120 onions in 30 minutes. Carl can chop 120 - 90 = 30 more onions than Brittney in 30 minutes.
This justifies what answer for what question? Q & A:
Brittney can chop 15 onions in 5 minutes. Carl can chop 20 onions within that same time. How many more onions can Carl chop in 30 minutes than Brittney?
30