12x+12 step by step below
First recognize that the unit rate we're finding is gallons per hour, or

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rate for Tank 1 = x gallons per hour = <em>a</em> gallons / <em>b</em> hours

rate for Tank 2 = y gallons per hour = <em>c</em> gallons / <em>d</em> hours
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The best and most correct answer among the choices provided by the question is <span>C. x over 520 = 5 over 13</span>.<span>
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Hope my answer would be a great help for you.</span>