Really need help with 5, 6, and 7. Im trying to do it in excel but it is giving me a wrong answer

Leslie Sporting Goods is a locally owned store that specializes in printing team jerseys. The majority of its business comes from orders for various local teams and organizations. While Leslie's prints everything from bowling team jerseys to fraternity/sorority apparel to special event shirts, summer league baseball and softball team jerseys are the company's biggest source of revenue. A portion of Leslie's operating information for the company's last year follows: Month January February March April May June July August September October November December Number of Jerseys Printed 185 205 195 510 615 685 435 325 380 265 260 190 Operating Cost $4,870 5,830 5,735 8,665 9,250 9,730 6,250 6,030 6,175 5,970 5,925 4,945 Required: 3. Using the high-low method, calculate the store's total fixed operating costs and variable operating cost per jersey. 4. Using the high-low method results, calculate the store's expected operating cost if it printed 420 jerseys. 5. Perform a least-squares regression analysis on Leslie's data. 6. Using the regression output, create a linear equation (y= a + bx) for estimating Leslie's operating costs. 7. Using the least-squares regression results, calculate the store's expected operating cost if it prints 650 jerseys