Three grades of milk are 1 percent, 2 percent, and 3 percent fat by volume. if x gallons of the 1 percent grade, y gallons of the 2 percent grade, and z gallons of the 3 percent grade are mixed to give x + y + z gallons of a 1.5 percent grade, what is x in terms of y and z ?
a. y+3zb. y+z/4c. 2y+3zd. 3y+ze. 3y+4.5z