Answer
$\approx$1h 7 min 34 sec.
Work Step by Step
Bolt's average speed in meters per second is $\displaystyle \frac{100}{9.69}\approx 10.32$ m/s.
Convert the marathon distance to meters:
$26$ miles = $23\displaystyle \cdot 5280\mathrm{f}\mathrm{t}\cdot\frac{1\mathrm{m}}{3.281\mathrm{f}\mathrm{t}}\approx 41840.9$ meters
The time needed to cover this distance at average speed of $10.32$ m/s is
$\displaystyle \mathrm{t}=\frac{41840.9}{10.32}=4054.4$ seconds
$=\displaystyle \frac{4054.4}{3600}\approx 1.126$ hours
=$1$ hour + $0.126(60)$min =$1$h $7.57$ min
=$1$h $7$ min +$0.57(60)$ s
$\approx 1$h $7$ min $34$ sec.
