Answer: 
====================================================
Work Shown:
The trick here is to first simplify the expression so that the 
term in the very lower denominator cancels out. This is to avoid dividing by zero. Once this division by zero error is avoided, we can replace the delta x term with 0 and evaluate the limit as approaches 0 from the right or positive direction.
First add 11 and 4 because you need to know how many he had in total 11+4=15 then divide 15 by 3 and then you have you answer 15/3=5.
There are 5 model cars in each pack.
