Angle 1 and angle 2 are what are called alternate angles. Two opposite angles between parallel lines. this means they are equal to each other.
So we have an equation: 2x + 20 = 3x + 10
Subtract 2x and 10 from each side
We now have 10 = x, so we know what x is
now plug in x to angle 1: (2 x 10) + 20 = 40, so angle 1 = 40.
