first of all your not making the equation clear but i will try and help you.
if u mean simplifying both equations then it is easy.
=> (sin3t) (t+2) = tsin3t+2sin3t
it is a simple cross muntilplication of both brackets
=> sin3t *t = tsin3t
=> sin3t * 2 = 2sin3t
Because of the + sign in (t+2), you add the cross multiplication.
therefore u get:
I hope this helps you