You can start by making a table that will permit you visualize the model. Start with 28,000 and subtract 700 hundreed step by step, in this way: 1) 28,000 - 700; 2) 28,000 - 2(700); 3) 28,000 - 3(700) ... then you can observe that after t hours the remaining number of gallos in the pool is 28,000 - 700t. So, the equation that models this situation is g(t) = 28,000 - 700t.