The increasing enrollment at Northern High School can be modeled by the equation N(t)= -t^2 + 25t + 600, where t represents the number of years after 2010. The increasing enrollment at Southern High School can be modeled by the equation E(t)= 24t + 570

so what's the question?

Do you want N(t) = E(t)?
do you want to know when N(t) stops increasing and starts decreasing?
Do you want to know why E(t) wasn't named S(t)?