It looks like you want to find the height of the green region. If so then that would be about 5.2 mL since the top part of the green area is around the first smaller tick above the 5.
Each smaller tickmark is 1/5 = 0.2 of a full unit. Note how there are 5 smaller tickmark spaces to make up a full unit (when we go from 5 to 6, there are 5 smaller tickmark spaces we have to move)
