Answer:
300 teenagers
Explanation:
Let
x -----> the number of children
y ----> the number of teenagers
z ----> the number of adults
we know that
x+y+z=1,200 ----> equation A
4x+5y+6z=5,300 ---> equation B
y/x=3/8
y=(3/8)x ----> equation C
Substitute equation C in equation A and equation B and solve for x,z
x+y+z=1,200 ----> x+(3/8)x+z=1,200 ---> (11/8)x+z=1,200 -----> equation D
4x+5y+6z=5,300 --> 4x+5(3/8)x+6z=5,300 --> (47/8)x+6z=5,300 --> equation E
Solve the system of equations D and equation E by graphing
(11/8)x+z=1,200 -----> equation D
(47/8)x+6z=5,300 --> equation E
The solution is the intersection point both graphs
The intersection point is (800,100)
see the attached figure
therefore
x=800 children
z=100 adults
Find the value of y
y=(3/8)x ----> y=(3/8)800=300 teenagers