Assuming a perfectly flat surface, this becomes another simple geometry problem. An incline of 12 degrees can be thought of as the bottom angle of a right triangle, where the corresponding opposite side is 500 meters long. The distance you then walk will be the hypotenuse of the triangle.
Using the same definition as yesterday, we know that sin(angle) = Opp/Hyp. We rearrange this to solve for the Hypotenuse and see that for this specific problem, the equation becomes:
Hyp = (500)/sin(12 deg)