could you please hurry i really need help this is a test

Answer:
BC = 20
Step-by-step explanation:
This is an isoceles triangle so AB = CB
If AB = CB then 3x = 5x - 20
3x - 5x= - 20
-2x = -20
x = -20/-2
x = 10
BUT length BC is 5x - 20
so 5(10) - 20
50 - 20
BC = 30