Hello alessandromangioneThe usual way of giving the grade of a hill is as a percentage. It is calculated from the formula:Percentage grade %If the incline is very small, this is approximately the same as:

Percentage grade %In the question you have been given, the vertical distance , and the distance along the slope . This is quite a steep incline, so it's not a good idea to use the second formula. So we use Pythagoras' Theorem to work out the horizontal distance:

Horizontal distanceSo, using the first formula:Percentage grade % %Grandad