Question

An adverting firm wishes to demonstrate to its clients the effectiveness of the advertising campaigns it has conducted. Using x as cost in millions of dollars: 3.5o, 3.05, 3.64, 1.59, 3.21, 2.12, 2.07, 3.99,1.58, 3.01, 1.36, 2.24; y for increases in sales: 6.89, 6.62, 6.73, 6.65, 6.49, 6.49, 6.81, 6.99, 6.29, 6.98, 6.42,6.63; and xy:24.115, 20.191, 24.4972, 10.5735, 20.8329, 13.7588, 14.0967, 27,8901, 9.9382, 21.0098, 8.7312, 14.8512. I have 12 recent campaigns to use for n and added all of x and divided by 12 to get 2.6133; and all of y's divided by 12 to get 6.6658; my equation looks like this 210.4856-(12)(2.36133)(6.6658)/(12-1) as (n-1), but I do not know how to get my sx or my sy (sx is my sample standard deviation of x values and y is my sample standard deviation of the y values). Can you help tell me how to get my sx and my sy sample standard deviations?