The number of significant figures in $4.870 \ m$ is

From the point of view of significant figures,which of the following is/are correct?
$(i)\ 11.3 \ cm + 4 \ cm = 15.3 \ cm$
$(ii)\ 4.53 \ m - 1.2 \ m = 3.3 \ m$
$(iii)\ 5.45 \ kg - 3.2 \ kg = 2.25 \ kg$
$(iv)\ 84.8 \ cm + 48.6 \ cm = 133 \ cm$

Time periods of oscillation of the same simple pendulum measured using four different measuring clocks were recorded as $4.62 \,s, 4.632 \,s, 4.6 \,s$ and $4.64 \,s$. The arithmetic mean of these readings in correct significant figures is: (in $\,s$)

An object of mass $m = 3.513 \ kg$ moves along the $x$-axis with a velocity of $5.00 \ ms^{-1}$. The magnitude of its momentum can be recorded as $...... \ kg \ ms^{-1}$.

The length of the side of a cube is $1.2 \times 10^{-2} \ m$. Its volume up to correct significant figures is

$A$ cube has a side of length $1.2 \times 10^{-2} \; m$. Calculate its volume.