Question 529784
By definition, a pair of supplementary angles are angles that add up to 180º. Remember that.

So let's call our two angles A and B.

Let  A+B = 180

And let  A = 18+B --->  A-B = 18

Then we have a system of equations.

A+B = 180
A-B = 18 

Notice if we added these two equations we would eliminate B. That's good.

2A  = 198

A = 99

Sub 99 back in for A.  99 + B = 180   Then B = 81.

Our two angles are 99 and 81.