An artificial lake is in the shape of a rectangle and has an area of 9/20 square mile. the width of the lake is 1/5 the length of the lake. what are the dimensions of the lake?

X=length
y=width
Area (rectangle)=length x width
we suggest this system of  equations:
y=x/5
xy=9/20
solve this system of equations by substitution method:
x(x/5)=9/20
x²/5=9/20
Least common multiple=20
4x²=9
x²=9/4
x=⁺₋√(9/4)
we have two solutions:
x₁=-3/2   it does not validate
x₂=3/2    ⇒y=x/5=(3/2)/5=3/10

The dimensions of the lake are:
lengh=3/2 miles
width=3/10 miles

to check:
Area=3/2 miles x 3/10 miles=9/20 miles².
width is 1/5 the length of the lake ⇒  3/10 miles=(3/2) /5 miles

Whose mistake? can you give more details to what the question is asking?