The rate of Fred making the balloons is:
rate = 17 balloons/ 15 minutes
We use this rate to solve this problem.
a. when time = 30 minutes
balloons = rate * 30
ballons = (17 balloons/ 15 minutes) * 30 minutes
balloons = 34 balloons
b. when time = 60 minutes
balloons = rate * 60
ballons = (17 balloons/ 15 minutes) * 60 minutes
balloons = 68 balloons