How to solve/integrate ∫ x √6+x dx by Algebraic Substitution

This sign: ∫ is for integral and this sign: √ (Alt+251) is for fraction. That's all I know so if you can help me to solve/integrate this problem you will help me a lot, thanks in advance.

u = 6+x => x = u-6
∫ x √6+x dx
= ∫ (u-6) √u du
= (2/5)u^(5/2) - 4u^(3/2) + c
= (2/5)(6+x)^(5/2) - 4(6+x)^(3/2) + c

u = 6 + x
x = u - 6
dx = du
∫(u - 6)√u du