Convert 20 minutes into seconds by multiplying 20•60=1200 because there are 60 seconds in a minute. Then, multiply 3•7=21 because one week has seven days. Next, subtract 1200-21=1179. To convert back into minutes, divide by 60 to get 19 and 13/20. Convert 13/20=?/60 because 60 seconds/minute and he final answer is 19 minutes and 39 seconds.