let x=Don's present age 2x=Chris's present age next year: x+1=Don's age 2x+1=Chris's age (x+1)+((2x+1)=4(x-1) (next year the sum of their ages will be four times as much as Don's age last year.) x+1+2x+1=4x-4 x=6 2x=12 Don's present age=6 Chris's present age=12