Answer
73 s
Work Step by Step
Let's take,
The average speed of the trip = $V$
Speed of the golf cart = $V_{1}$
Speed by walk = $V_{2}$
Distance by golf cart = $x_{1}$
Distance by walk = $x_{2}$
Time that the golfer rides in the golf cart = $t_{1}$
Time that the golfer walks = $t_{2}$
We can write,
The average speed $V=\frac{x_{1}+x_{2}}{t_{1}+t_{2}}=\gt t_{2}=\frac{x_{1}+x_{2}}{V}-t_{1}-(1)$
We can get,
$x_{1}=V_{1}t_{1}-(2)$
$x_{2}=V_{2}t_{2}-(3)$
(1),(2)=>(3),
$t_{2}=\frac{=V_{1}t_{1}+V_{2}t_{2}}{V}-t_{1}$
$t_{2}=\frac{V_{1}t_{1}-Vt_{1}}{V-V_{2}}$ ; Let's plug known values into this equation.
$t_{2}=\frac{3.1\space m/s\times28\space s-1.8\space m/s\times28\space s}{1.8\space m/s-1.3\space m/s}=73\space s$
Time that the golfer walks = 73 s
