Two angles that are supplements add up to 180°.
"The angle" is five times its supplement.
If I call the supplement 'S', then 'the angle' = 5S .
S + 5S = 180°
Combine like terms: 6S = 180°
Divide each side by 6 : S = 30°
The supplement of 'the angle' = 30°.
That's one of the choices.
"The angle" = 5S = 150°.
That's NOT one of the choices.