Answer
(a) $v_{av,x} = 1.5~m/s$
(b) $v_{av,x} = 1.2~m/s$
Work Step by Step
(a) $v_{av,x} = \frac{displacement}{time}$
$v_{av,x} = \frac{6.0~m}{4.0~s}$
$v_{av,x} = 1.5~m/s$
(b) $v_{av,x} = \frac{displacement}{time}$
$v_{av,x} = \frac{6.0~m}{5.0~s}$
$v_{av,x} = 1.2~m/s$