∠ 1 and ∠ 2 are supplementary angles, supplementary angles are two angles whose sum is exactly 180, therefore:
∠ 1 + ∠ 2 = 180
Where:
∠ 1 = 4y + 7
∠ 2 = 9y + 4
Replacing the data into the equation:
4y + 7 + 9y + 4 = 180
Add like terms:
13y + 11 = 180
Subtract 11 from both sides:
13y = 180 - 11
13y = 169
Divide both sides by 13:
y = 169/13
y = 13
Replace the value of y into ∠ 1 and ∠ 2
∠ 1 = 4y + 7 = 4(13) + 7 = 52 + 7 = 59
∠ 2 = 9y + 4 = 9(13) + 4 = 117 + 4 = 121