A body moving along a straight line uniform acceleration 'a' covers a distnace S1, the first t seconds and a distance S2 in the next t seconds, a is then given by
`(S_1+S_2)/t^2`
`(3S_1-S_2)/t^2`
`(S_1-S_2)/(t^2)`
`(3S_1-S_2)/(2t)`
explain the answer.