Answer:
The answer is 10.
Step-by-step explanation:
John works 2 more hours on the first day, so he starts with having 2 hours more than Gary.
He covers 4 hour for Gary, meaning John gained 4 hours and Gary lost 4 hours.
2 + 4 + 4 = 10
or
John begins with x hours which means that Gary worked x - 2 hours. John's total increases to x + 4 hours while Gary's to x - 6. Therefore, the total difference in hours is (x + 4) - (x - 6) = 10