I got this when I used substitution: a = 2200 – c

4(2200 – c) + 1.5c = 5050
8800 – 4c + 1.5c = 5050
The admission fee at a small fair is $1.50 for children and $4.00 for adults. On a certain day, 2200 people enter the fair and $5050 is collected. How many children and how many adults attended

8800 – 2.5c = 5050
–2.5c = –3750
c = 1500
a = 2200 – (1500) = 700

I'm a little confused on how to find where to use elimination and how to use it

It's simple :)

a + c = 2200... 1

1.5a + 4c = 5050... 2

Multiply the first equation by 4 for example, to give:

4a + 4c = 8800... 3

Now, subtract 2 from 3


4.0a + 4c = 8800
1.5a + 4a = 5050
2.5a + 0c = 3750


Then, solve 2.5a = 3750

:)