Heat Exchanger Calculation $($single shell $2-$pass$)$

$D_B($Bundle diameter$)=1\mathrm{.}11$m

$n_T($Total number of tubes required$)=1976$

Q: What does $n_D$ and $p$ mean on the slides and how can I calculate $n_D,Di($shell inside diameter$)$ and $c($clearance$)?$