Q$4.(5$ marks total$)$ Crystal directions and planes. Calculate the planar packing factor $($fractional area

occupied by atoms$)$ or the linear packing density $($atoms per unit length$)$ for the followings $(3$ marks

each$).$

$($a$)$ Planar packing factor for the $\{110\}$ plane in FCC$.(3$ marks$)$

$($b$)$ Linear packing density for the $[111]$ direction in BCC$.(2$ marks$)$