There is only condition given. It is that if you are under 12 years old, you pay $5. So our function is:
f(x) = 5 , x < 12
So just graph the above. It should just look like a horizontal line that goes from x = 0 to x = 12.
So graph the point (0,5) and (12,5) and connect a line between the two points.
The point (0,5) should be filled-in while the point (12,5) should be an open circle.