When two straight lines cut each other vertical angles are formed. There are two pair of vertical angles .Vertical opposite angles are always equal .
In the figure <TRS and <VRW are vertically opposite angles so they re equal.
<TRS=<VRW
Substituting the values of the angles given.
x+40=3x.
Subtracting x both sides.
40=3x-x
40=2x. Dividing both sides by 2.
X=20.