An isosceles triangle has 2 congruent (equal) base angles and one vertex angle .
The sum of the interior angles of any triangle is 180°.
So:
A+B+C = 180
Replacing:
A+48+ C = 180
A+C = 180-48
A+C = 132
Since both angles are congruent, divide the result by 2:
132/2 = 66
Base angles are 66° each