Greetings from Brasil...
We have 2 conditions:
1 - angles opposed by the vertex - the angles are equal
2 - supplementary angles - the sum of the two angles results in 180
2:
(4X + 15) and (5X + 30) are supplementary angles, so:
(4X + 15) + (5X + 30) = 180
9X = 180 - 15 - 30
9X = 135
X = 15
1:
(3Y + 15) and (5X + 30) are angles opposed by the vertex, so they are equal
3Y + 15 = 5X + 30
3Y = 5X + 30 - 15
3Y = 5X + 15 above we have already calculated the value of X
3Y = 5.(15) + 15
3Y = 75 + 15
3Y = 90
Y = 90/3
Y = 30
