Bailey can hit 42 golf balls in 3 1/2 hours. if she hits golf balls at a constant rate,

If Bailey can hit 42 golf balls in 3 1/2 hours, that is a fraction. 42 golf balls per 3 1/2 hours:
42 golf balls
3 1/2 hours
You want to make this number so it is how many golf balls per 1 hour(x is the number of golf balls:
x golf balls
1 hour
To get this number you would divide the numerator(the number on top), by the denominator(the number on the bottom). You would get 12 golf balls per hour.
12 golf balls
1 hour