A particles travelling in a straight line passesa fixed point O with a velocity of 1,5 m/s. It moves in such manner that , t seconds after passing O, its acceleration a m/s, is given by a = p + qt, where p and q are constants. Given that its velocity, is 3,5 m/s when t = 2 s, and that it comes instantaneously to rest when t = 3 s, calculate the value (p + q)