The circumference of a circle is given by the formula:
[tex]C=\pi d[/tex]Where d is the diameter of the circle.
If the circumference is 109.9 ft, we have:
[tex]\begin{gathered} 109.9=3.14\cdot d \\ d=\frac{109.9}{3.14} \\ d=35\text{ ft} \end{gathered}[/tex]So the diameter of the garden is 35 feet.