As this is tagged as a calculus question, we can take the rate v as an indication of rate of change of height x with time, t: dx/dt=2-0.1t. Integrate: x=2t-0.05t^2+k, where k is an initial distance from the ground when the balloon was released. If we assume that the balloon was released on the ground, then k=0. The height, x, after a period of time t is x=2t-0.05t^2.