math

(a + b)^6 will have 7 terms so you want row 6 of the triangle 1 6 15 20 15 6 1 
so (a + b)^6 = a^6 + 6a^(5)b + 15a^(4)b^2 + 20a^(3)b^3 + 15a^(2)b^4 + 6ab^5 + b^6 
given a = d and b = -5y 
∴ (d − 5y)^6 = d^6 + 6d^(5)(-5y) + 15d^(4)(-5y)^2 + 20d^(3)(-5y)^3 + 15d^(2)(-5y)^4 + 6d(-5y)^5 + (-5y)^6 
∴ (d − 5y)^6 = d^6 − 30d^(5)y + 3755d^(4)y^2 − 2500d^(3)y^3 + 9375d^(2)y^4 − 18750dy^5 + 15625y^6

Excellent, Hayley.....!!!