Finding probability density, mean and variance of Y=2X+3

Suppose X has a probability density given by:

$\displaystyle f(x)=\left\{\begin{array}{cc} \alpha e^{-\alpha x},&\mbox{for}\ x\geq 0\\0 & \mbox{ otherwise}\end{array}\right.$

1) Find the probability density of $\displaystyle Y=2X+3$

2) Find the mean and variance of $\displaystyle Y=2X+3$

Could someone please explain or refer me to someone website which explains the 'scale effects'. I tried reading it in my textbook, but don't really understand it.