Question

How long is a rectangular field with a width of 3/5 mile and an area of 21/50 square mile?

Answer 1

$w=\frac{3}{5}mi\\\\l=?\\\\A_{\fbox{ }}=w\times l;\ A_{\fbox{ }}=\frac{21}{50}mi^2\\\\\frac{3}{5}l=\frac{21}{50}\ \ \ \ \ |multiply\ both\ sides\ by\ \frac{5}{3}\\\\l=\frac{21}{50}\times\frac{5}{3}\\\\l=\frac{7}{10}\\\\Answer:\boxed{\frac{7}{10}mi=0.7mi}$

Answer 2

A = B*L

A = 21/50 sq miles
B =  3/5 mile
L = ? mile

L = A/B
L = (21/50)/(3/5)

* dividing by fraction is same as multiplying by it's reciprocal

L = (21/50)*(5/3)
L = (21*5)/(50*3)
L = 105/150

*divide both numerator & denominator by 5

L = 21/30

*divide both numerator & denominator by 3

L = 7/10 miles