(a+5b-4)^3

(a+5b-4)^3= 


(a+5b-4)(a+5b-4)(a+5b-4)= 


(a+5b-4)[a(a+5b-4)+5b(a+5b-4)-4(a+5b-4)]= 

(a+5b-4)[a^2+5ab-4a+5ab+25b^2-20b-4a-20b+16]= 

(a+5b-4)[a^2+10ab+25b^2-8a-40b+16]= 
a[a^2+10ab+25b^2-8a-40b+16]+
5b[a^2+10ab+25b^2-8a-40b+16]-
4[a^2+10ab+25b^2-8a-40b+16]= 


a^3+15a^2b-12a^2+75ab^2-120ab+48a+125b^3-300b^2+240b-64