Can someone please solve this MATH and Explain how you got the Answers? This is very confusing and I need help

Combine like terms to make a simpler expression 3z+z

Find the volume of the solid bounded by the plane z=0 and the paraboloid z=1-x^2 –y^2

The graph below shows the line of best fit for data collected on the number of cell phones and cell phone cases sold at a local electronics store on twelve different days. number of cell phone cases sold 50 * 0 5 10 15 20 25 30 35 40 45 number of cell phones sold which of the following is the equation for the line of best fit? a. y = 0.8x b. y = 0.2x c. y=0.5x d. y = 0.25x