If 6 machines make 6 wheels in 6 minutes, that means each of the machines must make 1 wheel in 6 minutes. If you now consider 30 machines, and we know each of these 30 machines makes 1 wheel in 6 minutes, that means all 30 machines will make 30 wheels in 6 minutes.
Fran can park for 6 hours! he has $7.50. if the first hour is $2 7.50-2=5.50. each hour is another $1. 5.50-1=4.50 4.50-1=3.50 3.50-1=2.50 2.50-1=1.50 1.50-1=.50. he is left with .50