Thank you Delta2 I think I am almost there, I found this problem in 'Calculus for Dummies' page181. I really should have used a metric based problem. I really appreciate your kind reply. Regards.
H(t) = t^3-6t^2+5t+30 this is a yo yo 30 inches above ground at t =0, at 4 secs it is 18 inches above ground. Please tell me how these figures are derived; t^3,6t^2, 5t; I realize the 30 is initial position. I am 81 but very curious. Thank you.