Salt in crude oil must be removed before the oil undergoes processing in a refinery. The crude oil is fed to a washing unit where freshwater fed to the unit mixes with the oil and dissolves a portion of the salt contained in the oil. The oil (containing some salt but no water), being less dense than the water, can be removed at the top of the washer. If the “spent” wash water contains 15% salt and the crude oil contains 5% salt, determine the concentration of salt in the “washed” oil product if the ratio of crud oil (with salt) to water used is 4:1.​