x + x + 2 + x + 4 = 21 {sum of three consecutive odd integers is 21}
3x + 6 = 21 {combined like terms}
3x = 15 {subtracted 6 from each side}
x = 5 {divided each side by 3}
x + 2 = 7 {substituted 5, in for x, into x + 2}
x + 4 = 9 {substituted 5, in for x, into x + 4}
5, 7, and 9 are the three consecutive odd integers