Using the Mono Crater, California map , Can you help me calculate the gradient of Mount Lewis?

Mono Crater, California map
I need to first place a straight edge object (e.g. ruler or piece of paper) on the map connecting Summit Lake to Parker Lake. Then using the statute mile scale bar, located on the bottom of the map, measure out 1 mile on a piece of paper.
Next, starting at the 10,800′ contour line near Summit Lake, measure out 1 mile (along the straight edge) using your scale markings on the piece of paper. Identify the elevation value at the end of your measurement.