A Rectangular Field Is Fenced in by Using a River $1,400$

Multiple Choice

A rectangular field is fenced in by using a river as one side. If $1,400$ m of fencing are used for the $240,000$ -m² field, find its dimensions.

A) $300 \mathrm {~m} \times 800 \mathrm {~m} , 400 \mathrm {~m} \times 600 \mathrm {~m}$
B) $450 \mathrm {~m} \times 900 \mathrm {~m} , 400 \mathrm {~m} \times 650 \mathrm {~m}$
C) $300 \mathrm {~m} \times 800 \mathrm {~m} , 450 \mathrm {~m} \times 600 \mathrm {~m}$
D) $300 \mathrm {~m} \times 1,000 \mathrm {~m} , 400 \mathrm {~m} \times 600 \mathrm {~m}$
E) $200 \mathrm {~m} \times 700 \mathrm {~m} , 500 \mathrm {~m} \times 700 \mathrm {~m}$