Let the length and breadth of the lawn be 5x and 3x m, respectively.
Now,
Area of the lawn = \(5x\times3x=5x^2\)
\(\Rightarrow \) 15x2 = 3375
\(\Rightarrow \) \(x=\sqrt{\frac{3375}{15}}{}\)
\(\Rightarrow \) \(x=\sqrt{225}=15\)
Length = 5x = 5x15 = 75 m
Breadth = 3x = 3x15 = 45 m
∴ Perimeter of the lawn = 2(Length + breadth)
= 2(75 + 45) = 2 x 120 = 240 m
Total cost of fencing the lawn at Rs 20 per meter = 240 x 20 = Rs 4800