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.

There are two straight sections, each 120 m long.

$$\text{Length of straight sections} = 2 \times 120 \text{ m} = 240 \text{ m}$$

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.

$$\text{Length of curved sections} = \pi \times 23 \text{ m} = 23\pi \text{ m}$$

The total distance is the sum of the lengths of the straight sections and the curved sections.

$$\text{Total distance} = 240 \text{ m} + 23\pi \text{ m}$$ $$\text{Total distance} \approx 240 + 23 \times 3.14159265... \text{ m}$$ $$\text{Total distance} \approx 240 + 72.25663 \text{ m}$$ $$\text{Total distance} \approx 312.25663 \text{ m}$$

Emmanuel runs at a constant speed of 4 m/s.
The formula for time is $\text{Time} = \frac{\text{Distance}}{\text{Speed}}$.

$$\text{Time} = \frac{312.25663 \text{ m}}{4 \text{ m/s}}$$ $$\text{Time} \approx 78.0641575 \text{ s}$$

$$\text{Time} \approx 78.1 \text{ s}$$

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