we know that
the average speed is equal to
[tex]average\ speed =\frac{distance}{time}[/tex]
in this problem we have
[tex]distance=1.50\ miles\\ time=143\ seconds[/tex]
substitute the values in the formula
[tex]average\ speed =\frac{1.5}{143}[/tex]
[tex]average\ speed =0.01\frac{miles}{seconds}[/tex]