In a triangle, the sum of interior angles is 180 degrees. So, to solve for y we can set up an equation for all of the angles
(2y) + (y + 10) + (50) = 180
From there, you can simplify it by combining like terms
3y + 60 = 180
Subtracting 60 from each side
3y = 120
And then dividing both sides by 3
y = 40
Meaning that the answer is D.
