From the data provided, we can conclude:
The perimeter of the rectangle is 60m, so:
[tex]60=2w+2l_{\text{ }}(1)[/tex]Where:
w = width
l = length
The width of the garden is 2/3 its length, therefore:
[tex]w=\frac{2}{3}l_{\text{ }}(2)[/tex]Replace (2) into (1)
[tex]60=2(\frac{2}{3}l)+2l[/tex]Solve for l:
[tex]\begin{gathered} 60=\frac{4}{3}l+2l \\ 60=\frac{10}{3}l \\ l=\frac{180}{10} \\ l=18 \end{gathered}[/tex]Replace l into (2):
[tex]\begin{gathered} w=\frac{2}{3}(18) \\ w=12 \end{gathered}[/tex]