A rectangular plot measuring 90 metres × 50 metres is to be enclosed by wire fencing. If thepoles of the fence are kept 5 metres apart, then how many poles will be needed? 

Correct option is B

Let's break this down step by step.

1. Find the perimeter of the plot:
   Since the plot is a rectangle with length = 90 metres and width = 50 metres, the perimeter is:
   ​$$2 \times (90 + 50) = 2 \times 140 = 280 \text{ metres}$$​​
   

2. Determine the number of poles:
   The poles are placed every 5 metres, meaning the number of poles required is:
   ​$$\frac{280}{5} = 56$$​​
   

Thus, the correct answer is (B) 56