Question 294407
Let L be the length and W be the width. 

"the width of a rectangle is half as long as the length"
{{{W=(1/2)L}}}
"the rectangle has an area of 128square feet"
{{{A=L*W=128}}}
but from above
{{{W=(1/2)L}}}
Substitute,
{{{L*W=128}}}
{{{L*(1/2)L=128}}}
{{{L^2/2=128}}}
{{{L^2=256}}}
{{{L=16}}}
Then
{{{W=(1/2)L=(1/2)(16)=8}}}
The rectangle is 8' x 16'.