I interpret the question as: "How far does he go before he stops?"
In this case the appropriate equation is v2 = u2 + 2as where v is final velocity (0), u is initial velocity (8.1m/sec), a is acceleration and s is distance.
The acceleration here is -9.8*sin(20°) m/sec2, the component of gravitational acceleration acting parallel to the slope (negative because it is retarding the skier).
0 = 8.12 - 2*9.8*sin(20°)*s
s = 8.12/(2*9.8*sin(20°)) metres
$${\mathtt{s}} = {\frac{{{\mathtt{8.1}}}^{{\mathtt{2}}}}{\left({\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{9.8}}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{sin}}{\left({\mathtt{20}}^\circ\right)}\right)}} \Rightarrow {\mathtt{s}} = {\mathtt{9.787\: \!286\: \!055\: \!842\: \!569\: \!1}}$$
s ≈ 9.8 metres