This question is based on the storm caused by this: https://twitter.com/ddmeyer/status/549965027948507136. Since a twitter discussion is not an objective question, I'll simply write out the key elements of the problem.
Movie earning estimates were reported as roughly \$15 million in total revenue across about 2 million transactions where the rental option was \$6 and the sale purchase option was \$15 dollars.
Emphasizing that the given number of transactions and revenue are rough estimates, can this be solved algebraically? That is, can the two "rough" equations (in whatever form that maybe) simply be solved to determine the two unknowns r and s (rentals and sales)? To be clear, r and s represent the number of transactions.
If solving these equations is valid, then what is the graphical explanation for why these two seemingly unrelated equations (one is # of transactions the other is revenue) can be solved?