Answer:
∠ B = 99°
Step-by-step explanation:
Supplementary angle sum to 180°
Sum A and B and equate to 180
3x - 12 + 4x - 25 = 180 , that is
7x - 37 = 180 ( add 37 to both sides )
7x = 217 ( divide both sides by 7 )
x = 31
Then
∠ B = 4x - 25 = 4(31) - 25 = 124 - 25 = 99°
