In this problem, we must start by remembering that an angle is considered a supplement only if it, and the other angle, add up to 180 degrees. So here, we know that:
Angle 1 (a1) and Angle 2 (a2) must add up to 180
Angle 1 (a1) is "10 less than half" of Angle 2 (a2) -> Here we have defined a2 as the supplement and a1 as the angle being asked for.
In equation form, we would consider these as:
a1 + a2 = 180, given that a1 = a2/2 -10.
We place the second equation into the first one, and we get:
a2/2-10 + a2 = 180
1.5a2 =190
a2 = 126.666° (you could round to 127°, if you wanted)
a1 = 53.333° (you could round to 53°, if you wanted) -> this is the answer