Answer:
Step-by-step explanation:
Let
x-----> the number of girls
y-----> the number of boys
we know that
-----> equation A
isolate the variable y
-----> equation B
Substitute equation B in equation A
Quadratic
y = ax^2 + bx + d
c (x) = ax^2 + bx + d
c (3) = a (3^2) + b (3) + d
c (3) = 9a + 3b + d = 15.50
c (7) = a (7^2 + b (7) + d
c (7) = 49a + 7b + d = 23.50
c (12) = a (12^2) + b (12) + d
c (12) = 144a + 12b + d = 56
solve using simultaneous equations... to get a b and d
use that to solve for x = 5
hope this helps?