Question

Sum of 1+2+3+5+6+7+8=320° what is the measure of 4

Answer 1

4=360-320
SO angle 4=40

Answer 2

Heya...

If it is the sum of any quadrilateral.
Then the measure of 4 = 360-(1+2+3+5+6+7+8)
As the sum of all angles of quadrilateral = 360°
So, 4 = 360-320
4 = 40°