How do you calculate stream gradient

Stream gradient=difference in height/elevation÷river/horizontal distance

Explanation:

The stream gradient is defined as the ratio between the elevation difference and the river distance.  

Stream gradient=difference in height/elevation÷river/horizontal distance

The rate of of discharge is directly proportional to the slope angle. This means that steeper the slope, the more is the discharge. It is generally calculated in terms of m/km or ft/miles. These stream gradients are prominent in the topographic maps as the elevations are provided in it.

i think the answer would be d