\(u=2x\Rightarrow du=2dx\Rightarrow d\left(2x\right)=2dx\Leftrightarrow dx=\dfrac{1}{2}d\left(2x\right)\)
\(\Rightarrow\int f\left(2x\right)dx=\dfrac{1}{2}\int f\left(2x\right).d\left(2x\right)=\dfrac{1}{2}.\left(2.2x.e^{2.2x+1}\right)+C=2x.e^{4x+1}+C\)