Question

Please check
Simplify
7t+3+t+9=8t+12

Simplify
m-2-4m-5=-3m+7

Solve
90=5t+t
90=6t
t=15

Answer 1

8t + 12 = 8t + 12 (identity)

-3m - 7 = -3m + 7 (Typo?)

yes, t = 15