A rectangular garden 45 m long and 30 m wide is to be fenced on all four sides, leaving a gap of 5 m for a gate. Fencing costs ₹120 per metre. What is the total cost?

The perimeter is $2(45+30)=150$ m, and the 5 m gateway needs no fence, so 145 m is fenced at $145\times 120$ = ₹17400. The trap ₹18000 fences the full 150 m and forgets the gate; ₹16800 takes the 5 m off twice, fencing only 140 m; ₹162000 charges the per-metre rate on the garden's AREA of 1350 sq m, but fencing is bought by length.