Answer:
y = 5
Explanation:
The 3 interior angles of a triangle sum to 180°
Sum the 3 given angles and equate to 180
100 + 4y + 25 + 3y + 20 = 180 ← simplify left side
7y + 145 = 180 ( subtract 145 from both sides )
7y = 35 ( divide both sides by 7 )
y = 5