What is the amount of sales tax owed on a $550 laptop computer if the tax rate is 7%?

We just started the introduction into circles and i have no idea how to do this.

If the scale factor between two circles is 2x/5y what is the ratio of their areas?

Find the volume of the solid whose base is the region bounded by f(x), g(x) and the x-axis on the interval [0, 1], and whose cross-sections perpendicular to the y-axis are squares. your work must show the integral, but you may use your calculator to evaluate it. give 3 decimal places for your answe