Respuesta :

"AB=BC" Meaning this is an isoceles triangle

Thus 
∠C is an angle Identical to ∠A
And given the rule of thumb; "every angle on a triangle. must add up to 180°"

∠A + ∠C = 130°
180° - 130° = ∠B

∠B = 50°
50 degrees is the measurement of a Angle b!

Good luck!