Hello, This is what am trying to solve A balloon is rising at the rate of 5ft/s. A boy is cycling along a straight road at a speed of 15ft/s.when he passes under the balloon it is 45 ft above him. How fast is the distance between the balloon and the boy increasing 3 seconds later Please let me know if am on the right path s^2=x^2+y^2 dy/dt = 5 dx/dt = 15 y= 45 so 2s ds/dt = 2x dx/dt + 2y dy/dt is this correct but also we can conclude that ds/dt = 15.81, but i think we have to find ds/dt. In the above equation am getting two unkowns thats were am getting stuck. Please help, thanks.