1. Expand (a+bx)^3

I done this and it I got
a^3 + 3a^2bx + 3ab^2x^2 + b^3x^3

2. The expansion of (1 - x)(a+bx)^3 in ascending powers of X begins 8 + 28x +.....

Find the values of a & b

I dont really understand this, could someone please show how you solve this?