To find the value of t, you need to isolate/get the variable "t" by itself in the equation:
25t - 87.5 = 12.5 Add 87.5 on both sides
25t - 87.5 + 87.5 = 12.5 + 87.5
25t = 100 Divide 25 on both sides to get "t" by itself
t = 4
PROOF
25t - 87.5 = 12.5 Substitute/plug in 4 into "t"
25(4) - 87.5 = 12.5
100 - 87.5 = 12.5
12.5 = 12.5