A running track is made from two straight sections and two semicircular sections. Emmanuel runs once around the track at 4 m/s. Calculate the time taken in seconds to 1 d.p.

Step 1: Calculate the total length of the straight sections. There are two straight sections, each 120 m long. $Length of straight sections = 2 \times 120 m = 240 m$

Step 2: Calculate the total length of the curved sections. The track has two semicircular sections. When combined, these two semicircles form one full circle. The diameter of this circle is given as 23 m. The circumference of a circle is given by the formula $C = \pi d$, where $d$ is the diameter. $Length of curved sections = \pi \times 23 m = 23\pi m$

Step 3: Calculate the total distance of one lap around the track. The total distance is the sum of the lengths of the straight sections and the curved sections. $Total distance = 240 m + 23\pi m$ $Total distance \approx 240 + 23 \times 3.14159265... m$ $Total distance \approx 240 + 72.25663 m$ $Total distance \approx 312.25663 m$

Step 4: Calculate the time taken to run one lap. Emmanuel runs at a constant speed of 4 m/s. The formula for time is $\text{Time} = \frac{Distance}{Speed}$. $Time = \frac{312.25663 m}{4 m/s}$ $Time \approx 78.0641575 s$

Step 5: Round the answer to 1 decimal place. $Time \approx 78.1 s$

The time it takes Emmanuel to run exactly once around the track is $\boxed{78.1 s}$.