Because we know the angles in a parallelogram add up to 360 degrees, we can add up values and divide to find x and y. 8y and 4x-20 are supplementary, they must equal the same value. Same with 10y and the other corner. By this, we can do 10y times 2 and 8y times 2 to get 16y plus 20y, or 36y. Then, we divide 360 degrees by 36. We get y=10 from this. Plug in 10 to 8y and get 80 as the upper left angle measurement. This means that 4x-20 equals 80. Add 20 to 80 on both sides so it cancels out and you get 100=4x. Simply divide and you will get x=25. To make sure this is right, plug all the numbers in and make sure all of the angles add up to 360. Hope this helps :)
