What is the percent error for the experiment below? Density Acquired: 9.01

Known Density 8.4

May someone me with these science questions

Estimate the molar mass of the gas that effuses at 1.6 times the effusion rate of carbon dioxide.

To prevent the presence of air, noble gases are placed over highly reactive chemicals to act as inert "blanketing" gases. a chemical engineer places a mixture of noble gases consisting of 4.37 g of he, 13.36 g of ne, and 36.65 g of kr in a piston-cylinder assembly at stp. calculate the partial pressure in torr of kr.