If there is a maximum of 10 grams of water vapor in a certain volume of air at 50 °, 20 grams at 60°F 30 grams at 70°F, 40 grams at 80°F. 50 grams at 90°F, and if the air contains 20 grams of water vapor at 90°F, what is the relative humidity in percent?

O 30%
O 40%
O 70%
O 50%
O 60%