The upward speed v(t) of a rocket at time t is approximated by v(t) = at2 + bt + c o s t s 100 where a, b, and c are constants. It has been found that the speed at times t = 5, t = 7, and t = 12 seconds are 100, 215, and 335 kilometers per second respectively. Determine the speed at time t = 15 seconds. (Use inverse matrix method)