Six gallons of a salt solution consists of 35% salt. It is the result of mixing a 40% solution with a 30% solution. How many gallons of each of the solutions was used? Let x= the number of gallons of the 40% solution and y= the number of gallons of the 30% solution. The corresponding modeling system is {x+y=60.4x+0.3y=0.35(6). Solve the system by using the method of substitution.