$\sum F y=0$

$\Rightarrow N - mg \cos \theta=0$

$\Rightarrow N = mg \cos \theta----(1)$

$Fx =0$ (as constant velocity $\Rightarrow$ No acceleration)

$\Rightarrow mg \sin \theta-\mu_{ k } N =0$

$\Rightarrow mg \sin \theta-\mu_{ k } mg \cos \theta=0$

$\Rightarrow \cos \theta\left(\tan \theta-\mu_{ k }\right)=0$

$\Rightarrow \mu_{ k }=\tan \theta=\tan 37^{\circ}=\frac{3}{4}=0.75$