Question 1110653
After trying to draw what you describe, it seems some of your labeling is wrong.  Best understanding seems to be  a top angle at the point B, and side b opposite and as a "bottom".  At the left on the bottom is point C; and at right on the bottom is point A.  Your interior angle at A is 40 degrees.    a=c=3.


Isosceles Triangle, so angle at C is also 40 degrees.


Angle at B?

{{{B+40+40=180}}}
{{{B=100}}}