First you must calculate the speed of Amy and speed of Bill.
[tex]
d=14.4km=14400m \\
t_a=40min=2400sec \\
t_b=20min=1200sec \\
s_a=\frac{d}{t_a}=\frac{14400m}{2400sec}=\boxed{6\frac{m}{sec}} \\
s_b=\frac{d}{t_b}=\frac{14400m}{1200sec}=\boxed{12\frac{m}{sec}} \\
[/tex]
Now calculate the difference between Bill's speed and Amy's speed.
[tex]
\Delta{s}=s_b-s_a=12\frac{m}{sec}-6\frac{m}{sec}=\boxed{6\frac{m}{sec}}
[/tex]
Amy's average speed is not faster. Bill's average speed is faster than Amy's by 6 m/sec.
Hope this helps.
r3t40
