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In my post, I will response part (a) only.
Enrollment at college A = 12500 + 800*(n-2011).
Enrollment at college B = 24200 - 500*(n-2011).
We want to know when it will happen = .
We write the equation
12500 + 800*(n-2011) = 24200 - 500*(n-2011)
We simplify it
800*(n-2011) + 500*(n-2011) = 24200 - 12500
(800+500)*(n-2011) = 11700
1300*(n-2011) = 11700
n - 2011 = 1170/1300 = 9.
The long-waited event will happen at the year 9 + 2011 = 2020. ANSWER
The number of enrolled students will be 12500 + 800*9 = 19700 = 24200 - 500*9 in each college. ANSWER
Solved.
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What is written next in your post - is a riddle to me . . .