#### Answer

a) $F_{a}$ = 3.6 N
b) $F_{b}$ = 0.4 N

#### Work Step by Step

$F_{net}$
= ma
= 8 $\times$ 0.5
= 4 N
$F_{a}$ + $F_{b}$ = 4 N
$F_{net}$
= ma
= 8 $\times$ 0.4
= 3.2 N
$F_{a}$ - $F_{b}$ = 3.2 N
$F_{a}$ - $F_{b}$ + 0.8 = $F_{a}$ + $F_{b}$
2 $\times$ $F_{b}$= 0.8
$F_{b}$ = 0.4 N
$F_{a}$ = 3.6 N