Both (4x+10y) and (6x) equal 90 degrees, as angle 4x+10y is vertical to a 90 degree right angle, and angle 6x is directly beneath the right angle, making it equivalent. To find x, you simply do 90/6, which is 15, meaning x=15. Now plug in that into 4x+10y=90, which will make it 60+10y=90. Subtract 60 from 90, and divide the difference, 30, by 10, giving you 3, thus showing that y=3. You can double check by plugging in the x and y values.
