Video Explanation

Text Explanation

This problem requires going carefully from words to math, and then setting up the equation, so we need to go one sentence at a time. The barrel starts  full, so we can call that , where C is the total capacity of the barrel. When k liters of liquid are added, it becomes  full, which is . To state that algebraically, when we add k to , we get , or

To solve, get the C values on one side

Find a common denominator for the fractions

and to solve for C, multiply both sides by the reciprocal of .  

and the answer is (C).