Hello!
Supplementary angles add up to 180. This gives us the system of equations below.
a+b=180
b= 4a+20
Now we plug our b value into the first equation and solve for a.
a+4a+20=180
We combine like terms.
5a+20=180
We subtract 20 from both sides.
5a=160
We divide both sides by 5.
a=32
Now we want to find our angle b. We can plug our a value into the equation.
b=4(32)+20
128+20=148
Therefore, our angle measure is 148°.
I hope this helps!
