The task is to generate the correct answer for a given math problem.
--------
Question: Problem: how many multiples of 7 are there between 10 and 100 ( both are inclusive ) ?

Answer: 13

Question: Problem: company x provides bottled water to its employees in 10 liter bottles , $ 2 each . at least how many 10 l bottles must company x buy monthly , so that new contract with $ 50 fixed monthly rate and $ 1 for 50 l bottle each paid off ? ( assume that no other costs apply )

Answer: 28

Question: Problem: if x / 4 years ago roger was 21 years old and x / 4 years from now he will be 4 x years old , how old will he be 5 x years from now ?

Answer:
7