Question

in the quadrilateral abcd, angle at a is 85°, angle at d is 83°, angle at c is 104°, find the measure of angle at b.

Explanation:

Step1: Sum of quadrilateral angles

The sum of interior angles of a quadrilateral is $360^\circ$.

Step2: Calculate unknown angle

Let the unknown angle at B be $x$. Then:
$x + 85^\circ + 83^\circ + 104^\circ = 360^\circ$
$x = 360^\circ - (85^\circ + 83^\circ + 104^\circ)$
$x = 360^\circ - 272^\circ = 88^\circ$

Answer:

88°