The sum of two consecutive even numbers is nine times their difference. What are these two numbers?

Answer 1

Sarah, it’s interesting that 8 and 10 also qualify.

if the second step had been translated using 2 as the difference (that is, (x+2)-x), then the equation would have been

2X+2 = 18

x = 8, x+2 = 10

so there are two sets of answers, both correct.

Answer 2

Let x and x+2 be 2 even numbers.

Then x + (x+2) = 9(x-(x+2))

2x+2 = -18

2x = -20

x=-10

Then -10 and -8 are the answers