By using suitable substitutions, find: \int 4 x\left(3 x^{2}+7\right)^{2} d x \int 5 x e^{\left(x^{2}+20\right)} d x \begin{aligned} &\text { (b) }\\ &\int e^{-x}\left(6+7 e^{-x}\right) d x \end{aligned} \text {

(d) } \int x \sqrt{(1+x)} d x \text { using } u=\sqrt{(1+x)}