Lines AB and AC are equal so you set up an equation like so...
4x + 1 = 2x + 23
Subtract 1 from both sides.
4x = 2x + 22
Subtract 2x from both sides.
2x = 22
Divide.
x = 11
Now you need to plug in 11 into 3x - 8.
3(11) - 8
= 33 - 8
= 25
So BC is 25.
I hope this helps love! :)