Answer
The speed will be 23 m/s at the bottom.
Work Step by Step
We can use a force equation to find the acceleration.
$ma = \sum F$
$ma = mg ~sin(\theta) - mg ~cos(\theta) \cdot \mu$
$a = g ~sin(\theta) - g ~cos(\theta) \cdot \mu$
$a = (9.80 ~m/s^2) ~sin(45^{\circ}) - (9.80 ~m/s^2) ~cos(45^{\circ}) \cdot (0.12)$
$a = 6.1 ~m/s^2$
$v_0 = (6.0 ~km/h)(\frac{1000 ~m}{1 ~km})(\frac{1 ~h}{3600 ~s}) = 1.67 ~m/s$
We can use kinematics to find the speed at the bottom.
$v^2 = v_0^2 + 2ax$
$v = \sqrt{v_0^2 + 2ax}$
$v = \sqrt{(1.67)^2 + (2)(6.1 ~m/s^2)(45.0 ~m)}$
$v = 23~m/s$
The speed will be 23 m/s at the bottom.