Lets use some variables:
x = number of adults
y = number of children
744 total people used the public swimming pool and the number adults and children are unknown, so, we can write an equation like:
x + y = 744
Since $2 are for adults, we can write that as 2x. Since $1.75 are for children, we can write that as 1.75y. Since the total price is $1,392.25, that's what the equation should equal. Equation:
2x + 1.75y = 1,392.25
Now, we have a system of equations.
~Rationalize equations
x + y = 744, 2x + 7/4y = 5569/4
~Isolate x for [ x + y = 744 ]
x + y - y = 744 - y
x = 744 - y
~Substitute with x
2(744 - y) + 7/4y = 5569/4
~Isolate y for [ 2(744 - y) + 7/4y = 5569/4 ]
2(744 - y) * 4 + 7/4y * 4 = 5569/4 * 4
8(744 - y) + 7y = 5569
5952 - 8y + 7y = 5569
5952 - y = 5569
5952 - 5952 - y = 5569 - 5952
-y = -383
-y/-1 = -383/-1
y = 383
~Substitute y with 383 in [ x = 744 - y ]
x = 744 - 383
x = 361
Therefore, there are 361 adults and 383 children.
Best of Luck!