Answer
$\mu_k = 0.21$
Work Step by Step
If the speed is constant, then the force of friction $F_f$ directed up the slope must equal the component of the skier's weight directed down the slope. Therefore,
$\sum F = ma = 0$
$mg ~sin(\theta) -F_f = 0$
$mg ~sin(\theta) -mg ~cos(\theta)\cdot ~\mu_k = 0$
$mg ~sin(\theta) = mg ~cos(\theta)\cdot ~\mu_k$
$\mu_k = tan(\theta) = tan(12^{\circ}) = 0.21$
The coefficient of kinetic friction $\mu_k$ is 0.21
