Answer:
420 students, 15 days after opening --make sure to check my work with calculators to be 100% sure mk :))
Explanation:
When will they be equal:
28x + 4 = -x² + 39x + 64
-x² + 11x + 60 = 0
This is a quadratic equation. That is why they wrote "day(s)" because there are two solutions for a quadratic equation so there may be two possible days in which the attendance was the same.
x = -4 or 15.
We can't have a "negative day" so we can ignore the solution of -4. In 15 days after the opening, the attendances will be the same.
Let's now solve for the actual attendance! You can use either equation to plug in 15 because in this case, the attendances are always going to be equal. Let's use the easier equation, though....
y = 28x + 4
= 28(15) + 4
= 420
The attendance will be 420 students and this will be 15 days after the opening.