Inside the four sided figure, the angles must add to 360. So 121+70+x+y = 360. You also know that a straight line is 180. This means 116 + y = 180. Using them together you can solve for the variables. Begin by substituting the equation 116 + y = 180 into the other equation.
The identity property of multiplication, also called the multiplication property of one says that a number does not change when that number is multiplied by 1. Ex. 12x1=12
