1. The problem states that the store made a $900 sale in the first month and plans to increase sales by $600 each month for 11 months. 2. We need to find the total sales during the first year (12 months). 3. The sales form an arithmetic sequence where the first term $a_1 = 900$ and the common difference $d = 600$. 4. The number of terms $n = 12$. 5. The sales in the $n$th month is given by the formula for the $n$th term of an arithmetic sequence: $$a_n = a_1 + (n-1)d$$ 6. Calculate the 12th month's sales: $$a_{12} = 900 + (12-1) \times 600 = 900 + 11 \times 600 = 900 + 6600 = 7500$$ 7. The total sales for 12 months is the sum of the arithmetic sequence: $$S_n = \frac{n}{2} (a_1 + a_n)$$ 8. Substitute the values: $$S_{12} = \frac{12}{2} (900 + 7500) = 6 \times 8400 = 50400$$ 9. Therefore, the total sales during the first year is $50400$ (rounded to the nearest whole number).