Question

a quadrilateral has three acute angle each measure is 80 degree what is the measure of the fourth angle​

Answer 1

sum of all angles of a quadrilateral = 360°

let the fourth angle be x

=> 80 + 80 + 80 + x = 360°

=> 240 + x = 360°

=> x = 360 - 240

=> x = 120°

hence, the 4th angle is 120°

Answer 2

Let the angle be x

$x + 80 + 80 + 80 = 360 \\ x + 240 = 360 \\x = 120$

The answer is 120°