#### Answer

$120\frac{3}{4}$ miles per hour

#### Work Step by Step

To find the average speed, divide the distance flown by the total travel time:
Speed
$\\=684\frac{1}{4} \div 5\frac{2}{3}
\\=\frac{4(684)+1}{4} \div \frac{3(5)+2}{3}
\\=\frac{2737}{4} \div \frac{17}{3}$
Use the rule $\frac{a}{b} \div \frac{c}{d} = \frac{[a}{b} \times \frac{d}{c}$ to obtain:
$\\=\frac{2737}{4} \times \frac{3}{17}
\\=\frac{2737(3)}{4(17)}
\\=\frac{8211}{68}
\\=120\frac{3}{4}$
The aircraft was flying at $120\frac{3}{4}$ miles per hour.