Answer:
6 ft longer (total length of 15ft)
Step-by-step explanation:
the initial dimensions are:
length: [tex]l=9ft[/tex]
width: [tex]w=8ft[/tex]
the area area of the garden is given by:
[tex]a=l*w[/tex]
so the original area is:
[tex]a=9ft*8ft=72ft^2[/tex]
Since we need the area to be [tex]120ft^2[/tex], and we can only change the length, the width will still be 8ft.
We substitute the value of the new area and the width to the equation for the area:
[tex]a=l*w\\120ft^2=l*8ft[/tex]
and we clear for the new length:
[tex]l=\frac{120ft^2}{8ft}\\ \\l=15[/tex]
The length of the garden for the area to be [tex]120ft^2[/tex], must be 15ft.
This means that if originally the length was 9 ft, now it has to be 6 ft longer.