A granular soil has a saturated unit weight of $20 \:kN/m^3$ and an effective angle of shearing resistance of $30^{\circ}$. The unit weight of water is $9.81 \: kN/m^3$. A slope is to be made on this soil deposit in which the seepage occurs parallel to the slope up to the free surface. Under this seepage condition for a factor of safety of $1.5$, the safe slope angle (in degree, round off to $1$ decimal place) would be ________