What is a lunar month?

When a micrometer screw gauge is used to find the thickness of a glass plate, the following observations were taken:
Pitch of the screw $=1 \mathrm{mm}$

Number of divisions on a circular scale $=100$

Reading on the main scale$= 0.3 \mathrm{cm}$

Reading on the circular scale $= {47}^{th}$ $\mathrm{division}$

Thickness of the glass plate in centimeter is 

The heart beats once in $\frac{4}{5} \mathrm{s}$. The heart beats $t\times {10}^9$ times in the life of a man. If we take the average life of a man $60 \mathrm{years}$, then the value of $t$ is ______.

Choose the correct answer from the given options ($2.365, 2.315, 2.45$).