The density of CO2 getting from experiment is 0.1/0.056 = 1.79 g/L. The percent error of this is (1.96 -1.79)/1.96*100%=8.67%. So the approximate percent error is 8.67%.
15% = 15 grams of solute in 100 mL solution
15 g --------------- 100 mL
?? ------------------ 1000 mL
1000 x 15 / 100 =
15000 / 100 => 150 g of solute
hope this helps!