#### Answer

(a) $a = 20~m/s^2$
(b) $a = 5~m/s^2$
(c) $a = 10~m/s^2$

#### Work Step by Step

$F = ma$ can be rearranged as;
$a = \frac{F}{m} = 10~m/s^2$
Then;
(a) $a = \frac{2F}{m} = (2)(10~m/s^2) = 20~m/s^2$
(b) $a = \frac{F}{2m} = \frac{10~m/s^2}{2} = 5~m/s^2$
(c) $a = \frac{2F}{2m} = \frac{F}{m} = 10~m/s^2$