Question

a quadrilateral has 3 equal angles each equal to 70 degree , find the fourth angle.

Answer 1

sum of the angles in a quadrilateral is 360 degree
3 angles os 210 degree
4th angle 360-210is 150 degree
therefore the fourth angle is 150 degree

Answer 2

the angle sum of a quadrilateral is 360 degrees 
so there are three equal angles which is 70 degree
so let the fourth angle be equal to x 
so 70+70+70+x=360
210+x=360
x=360-210
x=150
so you have found your fourth angle