Let x be the amount that Jeff spent for the food and medication of his dog. With this representation, the cost of food and medication for each cat is 2x/3 - 5. The equation that best represent the given situation is
x + 6(2x/3 - 5) = 195
The value of x from the equation is 45. Jeff spent $45
The equation is valid for positive values of x not greater than 40.
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Personally, I might put the domain at 1 ≤ x ≤ 40, because there's no point in using the equation (or parking the bus) if zero people are going on the trip.
