Assume that $t_{pd}$ is the average of $t_{PHL}$ and $t_{PLH}.$ Find the delay from each input to the output in Figure $2-41$ by

$($a$)$ Finding $t_{PHL}$ and $t_{PLH}$ for each path, assuming $t_{PHL}=0\mathrm{.}20ns$ and $t_{PLH}=0\mathrm{.}36ns$ for each gate. From these values, find $t_{pd}$ for each path.

$($b$)$ Using $t_{pd}=0\mathrm{.}28ns$ for each gate.

$($c$)$ Compare your answers from parts $($a$)$ and $($b$)$ and discuss any differences.