Use Ito's formula to compute the stochastic differentials dZ_t when: (W_t is a Brownian motion)
(a) Z_t = W_t^3,
(b) Z_t = int_0^t W_u^2 dW_u + int_0^t W_u du,
(c) Z_t = S_t^2 where dS_t = mu S_t dt + sigma S_t dW_t (mu and sigma are constants),
(d) Z_t = exp(4S_t) where dS_t = 2dt + 3dW_t,