The measure of a single angle of a triangle is not enough information to allow you to find any other angle or side length of the triangle. Is there more information or a figure?
If this triangle is a right triangle, and angle C is the right angle, then angle C measures 90.
The sum of the measures of the angles of a triangle is 180.
m<A + m<B + m<C = 180
We know angle A measures 48.
Angle C measures 90.
48 + m<B + 90 = 180
m<B + 138 = 180
m<B = 42