Hello, thank you for taking the time to post your question!
To find the total enrollment function you just want to add together each individual high school value to get the overall total. For this one that means taking
Total = f(t) + g(t)
Total = 32t + 1255 + 27t + 1380
Total = 59t + 2635
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)