Short Answer: y = 40
Remark
Bisect means cut's in half. So that means that the two angles are each 1/2 of the whole angle and are equal.
Step One
Set up the equation
y + 30 = 3y - 50 Subtract y from both sides.
30 = 3y - y - 50
30 = 2y - 50 Add 50 to both sides.
30 + 50 = 2y
80 = 2y Divide by 2
80/2 = y
y = 40
check
y + 30 = 3y - 50
40 + 30 = 3(40) - 50
70 = 120 - 50
70 = 70 and it checks.