(2x-3)(4x squared-x-10)=8x cubed-14 squared+Bx=30
What is the question? Are you supposed to solve for B?
Is your second = (after BX) supposed to be a plus sign? I think so.
The terms on the left multiply out to
8x^3 -14 x^2 -23x +30
Comparing that with what is on the right may tell you what B is.
You need to be more careful reading your problems and stating your questions.