We know that angle C and angle A are congruent because this is a parallelogram. We also know that in a triangle, all the angles add up to 180.
Looking at triangle ABD (or ABY, depending on how you look at it), angle A is 63 degrees and angle B is 72 degrees. To find out angle y, we subtract 72 and 63 from 180.
180-72-63
=45
Therefore, angle y is 45 degrees.
I hope this helps!
