Question

Find the value of x in each quadrilateral.

Answer 1

bearing in mind that the sum of all interior angles in a polygon is

180( n - 2 ),  n = number of sides in the polygon.

well, this one is a quadrilateral, it has 4 sides, so n = 4, so the total amount for all interior angles will be 180( 4-2) = 360°, that means

$\bf 57+97+131+(15+4x) = 360\implies 300+4x=360 \\\\\\ 4x = 60\implies x = \cfrac{60}{4}\implies x = 15$