Find the measure of b, given m∠a = 38°, m∠b = 74°, and a = 31.

b = 48.4017

Explanation:
For this question, we will use the sine rule to get the missing side b. The sine rule is shown in the attached image.
We are given that:
a = 31
measure angle A = 38°
measure angle B = 74°

Substitute in the relation as follows:
sinA/a = sinB/b
sin(38) / 31 = sin(74) / b
b = [sin(74)] / [sin(38) / 31]
b = 48.4017

Hope this helps :)