Answer:
14 minutes
Step-by-step explanation:
Ⓗⓘ ⓣⓗⓔⓡⓔ
Well, what I do for these problems is do 1/x with x being the amount of time given.
1/21+1/42=3/42
3/42=1/14
Together, they would take 14 minutes!
(っ◔◡◔)っ ♥ Hope this helped! Have a great day! :) ♥