Wcos12 is the component of the weight perpendicular to displacement. Wsin12 is the component of the weight

*in* the direction it's moving. Making a sketch often helps.

$\displaystyle W_w=mgsin(12) \cdot s=5,0 \cdot 9,8 \cdot sin(12) \cdot 1,5 \approx 15,3 \ J$