a) The binomial expansion of (1-2x)^-3 up to the term in x^3 = 1+6x+24x^2+80x^3

b) hence find the first three terms of the expansion for 1-3x/(1-2x)^3

what is the relation? I know (1-2x)^-3 = 1/(1-2x)^3

so how do you find the first three terms of 1-3x/(1-2x)^3 by knowing part a)?