The measures of two supplementary angles have a ratio of 5 : 4. what is the measure of the larger angle

Supplementary angles add to 180
let x and y represent the two angles

x + y =180°

and if the ratio is 5:4, we can represent the angles by
x = 5a
y = 4a

5a + 4a = 180°
then solve for a
9a = 180°
a = 20°

x = 5(20)
y = 4(20)

so the two angles are 
100° and 80°