add s and t, multiply the result by u, then add r to what you have

add s and t, multiply the result by u, then add r to what you have.

Take this algebraic expression in 3 parts:

1. Add s and t: s + t
2. Multiply the result by u means me multiply (s + t) times u: u(s + t)
3. Then add r to what you have. what you have means the result in #2.

u(s + t) + r