Angles on a straight line add up to 180° This means we can say that:
(5x + 20) + (4x +25) = 180
Now we have an equation that we can solve:
(5x + 20) + (4x +25) = 180 9x + 45 = 180 <em>(we collected the terms : 4x + 5x = 9x, and 20 + 25 = 45)</em> 9x = 135 <em>(we subtracted both sides by 45, to get the x values alone on one side) </em>x = 15 <em>(we divided both sides by 9, to get what just x is) </em><em>-------------------------------------------------------------------------------------------------------------
</em>Now that we know the value of x, we can substitute it into the equations given in the diagram: