Charlie runs at a speed if 3 yards per second. About how many mph dies charlie run?

(3 yard/sec) x (3600 sec/hour) x (1mile/1760 yard) = 6.136 mile/hour (rounded)

1760 yards = 1mile

1 yard = 1/1760 miles

3 yard = 1/1760*3 miles

= 0.0017 miles

now,

1 hour = 60 minutes

= (60 * 60) seconds

= 3600 seconds

so

1 second = 1/3600 hour

so charlie travels at the speed of 0.0017 / (1/3600) mph

= 6.12mph