Answer:
Dan is 29. Cary is 36.
Explanation:
Let Dan's age now be D.
Let Cary's age now be C.
"Cary is 7 years older than Dan."
C = D + 7
"In 7 years the sum of their ages will be 79. "
In 7 years, the ages of Dan and Cary will be D + 7 and C + 7, respectively.
D + 7 + C + 7 = 79
C + D + 14 = 79
C + D = 65
C = D + 7
The last two equations in bold above form a system of equations. Since the second equation is already solved for C, we use the substitution method.
D + 7 + D = 65
2D + 7 = 65
2D = 58
D = 29
C = D + 7
C = 29 + 7
C = 36
Answer: Dan is 29. Cary is 36.