10. This weekend, Martha has time to read 40 pages of economics and 30 pages of sociology. Alternatively, she could read 10 pages of economics and 90 pages of sociology. Which of these equations describes all combinations of economics, E, and sociology, S, that she could read over the weekend?
(A) E/2 + S = 50
(B) E + S = 100
(C) E + S = 70
(D) 2E + S = 110
(E) none of the above.
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