The other guy answered correctly, but with no explanation. So I will try to explain why. This is a system of equations. You know J( Jack) is 10 years older than P( Priscilla). So J = P + 10. You also know they both add up to 172. So J + P = 172. To solve for P, get J by itself. In the 2nd equation, just subtract P from both sides to get J = 172- P. Now put the second parts together to get P + 10 = 172 - P. Add P to get 2P + 10 = 172. Now subtract 10 from both sides to get 2P = 162. Divide both sides by 2 to get P = 81. To get J, replace P in the first equation to get J = 81 + 10 = 91. Now you can check with the second equation. 91 + 81 = 172. So J = 91, and P = 81.