Use Pascal's triangle to expand the binomial.
(d - 5y)^6
Hmm.. Interesting, I have not learned that yet O_O.
And I don't think I ever want too!
d^6-30 d^5y+375 d^4y^2-2500 d^3 y^3+9375 d^2 y^4-18750 dy^5+15625 y^6
