What is the answer for this question??

Which expression is equivalent to (3^2)^-2 a.-81 b.-12 c.1/81 d.1/12

What number should be added to both sides of the equation to complete this square? x^2-10x=7

At the electronics store you have a coupon for 20% off up to 2 cds you buy for cds with the original cost of $10.99 each the sales tax is 5% what is the total cost of your purchase