We know that the sum of the interior angles of a triangle adds up to 180 degrees.
We have two angles in the given triangle as y and one of the angles is equal to 72 degrees. We can set up an equation where all of these angles add up to 180 degrees and then solve for y.
72 + y + y = 180
72 + 2y = 180
Subtract 72 from both dies of the equation.
72 - 72 + 2y = 180 - 72
2y = 108
Divide both sides by 2.
2y / 2 = 108 / 2
y = 54 degrees