#### Answer

(a) $a = 4~m/s^2$
(b) $a = 16~m/s^2$
(c) $a = 8~m/s^2$

#### Work Step by Step

$F = ma$ can be rearranged as;
$a = \frac{F}{m} = 8~m/s^2$
Then;
(a) $a = \frac{(F/2)}{m} = \frac{8~m/s^2}{2} = 4~m/s^2$
(b) $a = \frac{F}{(m/2)} = (2)(8~m/s^2) = 16~m/s^2$
(c) $a = \frac{(F/2)}{(m/2)} = \frac{F}{m} = 8~m/s^2$