How to integrate (x^6-7x)^4

A = ∫(x^6-7x)^4dx
A = ∫[(x^5-7)x]^4dx
A = ∫(x^5-7)^4 x^4dx
we take
u = x^5-7
du = 5x^4 dx
du/5 = x^4 dx
hence:
A = ∫(x^5-7)^4 x^4dx
A = ∫(u)^4 du/5
A = 1/5 ∫u^4 du
A = 1/5 [1/5u^5] + c : c is constant
A = 1/25 u^5 + c
A = 1/25 (x^5 - 7)^5 + c

I = ∫ (x^6-7x)^4 dx

=> I = ∫ (x [ x^5 - 7 ] ) ^4 dx

=> I = ∫ x^4 (x^5 - 7)^4 dx

=> I = (1/5)* ∫ (x^5 - 7)^4 (5x^4dx)

put t = x^5 - 7 => dt = 5x^4 dx

=> I = (1/5) * ∫ t^4 dt

=> I = (1/5) * (t^5)/5 + c ...............using ∫x^n dx = [x^(n+1)]/(n+1) + c

=> I = (1/25)*(x^5 - 7)^5 + c

which is the answer!