First we find the total change and then we divide by the time.  We subtract the final count from the intial number to find the total change.  When the park opened the turnstyle read 1278 and 7 hours later the count read 3672 so we have 3672-1278= 2394.  Now we take the difference and divide it by our units of time, in this case 7 hours.  2394/7= 342.  Using this we know that there are 342 people going through the turnstile per hour.