ok so i got this packet in math class about speed of light/sound and there is level 1 and 2 and Einstein level. i got to the 2nd Einstein level question and got stuck and i was wondering if anyone could help. here it is:

You see lightning flash in the north and 7.5 seconds later you hear thunder. Twelve minutes later you see lightning in the south and 12.5 seconds later you hear thunder. how fast is the storm moving?