so a mile is 5280 ft, and if the are is 9/20 of a miles than find the miles area which is: 27878400 ft squared. then multiply the number by 9/20. and you get 12545280 ft squared.
Now that we have the Area: 12545280
Length is 9/10 of a mile. so 9/10x5280= 4752
L x W= A
4752W=12545280
Divide so you get W= 12545280/4752.
which is equal to 2640ft= W