Hey there!
A quadrilateral has 360 degrees. So add all the degrees together to 360. 9x+1+5x-12+8x+61+90=360. 90 degrees is in the bottom left corner. Combine like terms. 22x+140=360. Subtract 140 from each side. 22x=220. Divide 22 on each side to get x=10. Plug in 10 for x in angle D. 5(10)-12=38. The measure of angle D is 38 degrees.
I hope this helps!