(a+5b)^5 = a^5 + 5a^4 5b + 10a^3 (5b)^2 + 10a^2 (5b)^3 + 5a (5b)^4 + (5b)^5
(a+5b)^5 = a^5 + 25a^4b + 250a^3b^2 + 1250a^2b^3 + 3125ab^4 + 3125b^5
(a+5b)^5 = a^5 + 5a^4 5b + 10a^3 (5b)^2 + 10a^2 (5b)^3 + 5a (5b)^4 + (5b)^5
(a+5b)^5 = a^5 + 25a^4b + 250a^3b^2 + 1250a^2b^3 + 3125ab^4 + 3125b^5