Shelby completes one lap of a go-cart track every 40 seconds. Laura completes one lap of the
same track every 30 seconds. Suppose Shelby and Laura cross the starting line at the same time.
a. How many seconds will pass before they cross the starting line at the same time again?
b. How many laps will Shelby have completed in that time?
c. How many laps will Laura have completed in that time?