Don't know how to solve Unit Step Function

Question

This is the solution that i found in the solution sheet but i can't seem to know how to get to the step that is in the red rectangle.

Answer 1

We started with $$2[u(t) - u(t-1)] + (3 - t)[u(t-1)-u(t-3)].$$

Distributing we get,

\begin{align} 2u(t) - 2u(t-1) + (3 - t)u(t-1)-(3-t)u(t-3) &= 2u(t) - 2u(t-1) + 3u(t-1) - tu(t-1)-(3-t)u(t-3)\\ &=2u(t) + u(t-1)-tu(t-1) -(3 - t)u(t-3)\\ &=2u(t) -(t-1)u(t-1)-(3-t)u(t-3). \end{align}

Hope this helps.