One tank holds 60 litres and is gaining 8 litres a minute. Another holds 200 litres and is losing 6 litres a minute. After how long do the two hold the same volume?

1. Write the first tank as V = 60 + 8t, with V in litres and t in minutes. 2. Write the second tank as V = 200 - 6t. 3. The volumes match when 60 + 8t = 200 - 6t. 4. Add 6t to both sides to get 60 + 14t = 200, then take 60 from both sides to get 14t = 140. 5. Divide by 14 to get t = 10 minutes, and both tanks then hold 140 litres. 6. Option D comes from dividing the 140 litre gap by 7 rather than by the combined 14 litres a minute. _Source: OpenStax College Algebra (CC BY 4.0), Ch 7 "Systems of Equations and Inequalities", section 7.1 Systems of Linear Equations: Two Variables_