Equation for slope=1/3 and y-intercept=-1 is:
y = mx + b
where m is slope and b is y-intercept.
So, equation becomes
y = -1x + 1/3
Now put different values of x in the equation to get corresponding value of y.
x y
0 1/3
1 -2/3
2 -5/3
3 -8/3
-1 4/3
-2 7/3
-3 10/3
~Hello There!~

Rearrange for s

After 8 years, the new equation would be:

Cross multiply

Subtract 8

Substitute old equation

Solve to get m as 16.
s = 40.
Their current ages are 16 and 40 and the different is 24 years. Therefore, Caitlin is correct.
Hope This Helps You!
Good Luck :)
Have A Great Day ^_^
- Hannah ❤