There is 180 degrees in a triangle so it is 80 degrees
Remember y ou can do anything to an equation as long as you do it to both sides
get 1x by itself
8x-12=4x+24
add 12 to both sides
8x=4x+36
minus 4x from both sides
4x=36
divide both sides by 4
x=9
It's 21 square units. If you map it on a complex plane (x-axis is real numbers, y-axis is imaginary numbers) you'll see that the sides of the rectangle is 3 and 7 which multiply to 21.