Round off to 3 significant figure.
20.96

Explanation

(i) 20.96 has four significant figures. The fourth significant figure is more than 5 and hence on rounding off to three significant figures, the given measurement will become 20.9 +0.1 i.e., 21.0.
(ii) 0.0003125 has four significant figures. The fourth Significant figure is 5 and hence on rounding off to three Significant figures, the given measurement will become `0.000312` or `3.12xx10^(4)` . This is because 2 before 5 is an even number .