a + 4c = 19
2a + 2c = 17
We can do this a few ways, but since we have a single a in the first equation, I would "solve" the 1st equation for it.
a + 4c - 4c = 19 - 4c
a = 19 - 4c
Now, two things that are equal are interchangeable, so we can put 19 - 4c in the 2nd equation for a.
2(19 - 4c) + 2c = 17
38 - 8c + 2c = 17
-6c = -21
c = 3.5
Hey, we have the value for c, which we'll turn into a money amount at the end. Let's plug it into the first equation to find a.
a + 4(3.5) = 19
a + 14 = 19
a + 14 - 14 = 19 - 14
a = 5
So, an adult ticket costs $5 and a child's ticket costs $3.50.
