Question 653509
Let's call Juan's age "J". Carl is 4 years older, so his age will be called "J+4." Their ages add up to 18, so J +  (J+4) = 18. So, 2J+4=18, 2J=14, J=7. This means Juan is 7, so Carl is 7+4, or 11. Check by making sure those ages add up to 18, as stated in the problem.