To find out how long she takes to solve 5 problems, we need to divide the time by 5.
5 into 11 goes 2 and 1 minute over. A minute is 60 seconds, so we add 60 to 20 to get 80, then we divide by 5, so that's 16 seconds. Therefore the time taken to solve one problem (on average) is 2 minutes 16 seconds.