How long will a boy take to run around a square field of side $35\text{meters}$, if he runs at the rate of $9\text{km/h}$?

First, find the total distance to be covered, which is the perimeter of the square field:
$$\text{Perimeter}=4\times \text{side}=4\times 35\text{m}=140\text{m}$$

Next, convert the running speed from kilometers per hour ($\text{km/h}$) to meters per second ($\text{m/s}$):

$$\text{Speed}=9\times \frac{5}{18}\text{m/s}=\frac{5}{2}\text{m/s}=2.5\text{m/s}$$

Now, compute the time taken using the formula:

$$\text{Time}=\frac{\text{Distance}}{\text{Speed}}$$

$$\text{Time}=\frac{140}{2.5}=\frac{140}{\frac{5}{2}}=\frac{140\times 2}{5}=28\times 2=56\text{seconds}$$