6, -15+6=-9
I don’t really know an explanation but it’s easy
Seven and six hundred- thirty-two thousandths.
The angles in a isosceles triangle add up to 180 degrees.
so 180 degrees take away 36 degrees = 144 degrees.
base angles in a isoceles triangle are equal so 144 divided by 2 = 72 degrees.
so to find out y you do 360 - 72 = 288 degrees
therefore y = 288degrees