How do you solve this?

8-2(t-1)=t+7 The answer is suppose to be 1

u-8-3u=2u+7 The answer is suppose to be -15/4

Combine terms and the put only u (or t) on one side of the equation, and combine constants on the other.

Example, with steps:
u-8-3u = 2u+7
Add 2u and -7 to both sides of the equation.
-15 = 4 u
u = -15/4