I need help with this ​

How can you tell when x and y are not directly proportional?

What is the geometric mean of 3 and 7? a) square root of 21 b) 2 square root of 6 c) 2 square root of 7 d) 21

Martha is training for a duathlon, which includes biking and running. she knows that yesterday she covered a total distance of over 55.5 miles in more than than 4.5 hours of training. martha runs at a speed of 6 mph and bikes at a rate of 15.5 mph.