Find in ascending power of t, the first three terms in

Find in ascending power of t, the first three terms in expansions of a. (1 + at - bt^2)^3 b. (1 - at + bt^2)^3 Hence find, in terms of a and b, the coefficient of t^3 in expansions of (1 + at - bt^2)^3 (1 - at + bt^2)^3.