Please help, quick math, and a short explanation on how you got the answer! Thank you!!

Answer:
this is an iscoceles triangle.
I know this because 2 of the sides are equal in length
Therefore,
AB=AC
3x-5=-2x+15
x-5=15
x=20
if x=20 then BC=2(20)
BC=40
Step-by-step explanation: