Johnny was playing baseball with his friends and they noticed a bolt of lightning. they heard thunder seven seconds later. how far away is the storm?

That particular strike was very roughly 2.4 km (1.5 miles) away from them.

That's if you use 340 m/s (1120 ft/sec) for the speed of sound. 
But the air in the region for several thousand feet around a thunderstorm
is doing weird things to sounds that pass through it, so you can't use any
exact number for the speed of sound in a stormy area.

The only thing you can be absolutely sure of is that Johnny and his friends
need to round up their equipment and get in the house.  NOW !