Question

three angles of a quadrilateral are 80°,70°,120°, the fourth angle is ​

Answer 1

SINCE ,the sum of all angles of quadrilateral is 360°

so let"s assume the fourth angle be x

so ,  80°+70°+120°+x=360°

       270+x=360°

         x=90°

so fourth angle is 90°

Answer 2

80° + 70° + 120° + 4rth angle = 360
270+ 4rt angle= 360
4rth angle= 360-270
= 90