Basically, what's the equation/formula for [p]subscriptB?

Here's my work for finding [p]subscript B:

I have the equation p(x)=3-8x+2x^2-6x^3 and B=(1+x+x^2+x^3, 1+x+x^2, 1+x, 1).

I said a(1+x+x^2+x^3)+b(1+x+x^2)+c(1+x)+d=3-8x+2x^2-6x^3.

I solved for a,b,c,d and got:

a=-6

b+a=2

a+b+c=-8

a+b+c+d=3

Thus, a=-6, b=8, c=-10, d=11.

So I said that [p]subscriptB is the vector:

[-6

8

-10

11]

, but this is obviously not right.

Any help or guidance would be greatly appreciated.