Since the quadrilateral has 90 degree angles, it must be a a square or a rectangle. This means the measure of sides left and right are the same and the measure of sides top and bottom are the same.
To get the measure of y, you can use left and right or top nd bottom.
I'll use left and right. 10=2y+4 => 10-4=2y => 6=2y => y=3
You can check it by substituting. 2(3)+4=10 The answer is the measure of the right side, which is the same as the measure of the left side.
