The line BD is divided into two smaller segments by point C.
If you add those smaller segments, the result will be equal to the length of segment BD:
BD=BC+CD
Replace this expression with the given equaities and you'll be able to determine an equation:

Next perform the calculations between all alike terms:

And rearrange them so that all x-related terms are on the left side and the other terms on the right side of the equation
