Given the placement of the ∠x, we can see that the angles of 42°, 90° and x all form a straight line, which by definition has a total angle measure of 180°. In order to find 'x', we can set up the sum of these three angles and solve for 'x':
42 + 90 + x = 180
132 + x = 180
Subtract 112 from both sides: 132 + x - 132 = 180 - 132 or x = 48
