[tex]In\ 1min\ Al\ wash\ \frac{1}{6}\ car.\\In\ 1min\ Fred\ wash\ \frac{1}{8}\ car\\\\Together\ in\ 1min:\frac{1}{6}+\frac{1}{8}=\frac{4}{24}+\frac{3}{24}=\frac{7}{24}\ car\\\\Answer:Al\ and\ Fred\ wash\ the\ car\ in\ \frac{24}{7}min=3\frac{3}{7}min\approx3.5min[/tex]