### If a:b = 2:3, find b.

108°

Step by Step Explanation:
1. Since, both a and b lie on a straight line, we can say that the sum of a and b is equal to 180.
2.
 a b
=
 2 3
, cross multiplying the fractions, we get, 2b = 3a, or b =
 3a 2
.
3. On substituting this value in a + b = 180, we get: a +
 3a 2
= 180, or
 5a 2
= 180, or a = 180 ×
 2 5
, or a = 72 degree.
4. On substituting this value in a + b = 180, we get:
72 + b = 180
So,  b = 180 - 72
b = 108°
.
5. Hence, the values of the asked angles a and b are 72° and 108° respectively.