Because both sides are given as 10, the two bottom inside angles would be the same.
Since one of the bottom angles is given as 74 degrees, the other bottom angle is also 74 degrees.
The total of those two angles is : 74 +74 = 148 degrees.
The total of the 3 inside angles of a triangle is 180 degrees.
The top angle (B) is 180 - 148 = 32 degrees.
The answer is B.