Question

Find the percent error of this: The experimental value was 2.8 g/cm^3 and the theoretical value was 2.70 g/cm^3. What I'm confused on is that I know you're supposed to do 2.70 - 2.8 over 2.70 then times 100. But like sig figs, do you do it at the end? Or do you 2.7 - 2.8 = -0.1 (sig fig) THEN -0.1/2.70 = -0.037037 x 100 = -3.7037 rounds to 1 sig fig = -4 %? I know in this problem doing sig fig at the top of the fraction or at the end give the same result but my point here is WHEN DO YOU DO SIG FIGS? I'm very confused/