1:4. 16 is 25% of 64, or 1/4, this translates to 1:4 in ratio form.
I can help but can you tell me what kind of problem your doing.
A geometric figure enclosed by a circle is called an inscribed figure.
It would take 2 hours. To complete the whole lawn you would need:

To make a whole, so to get that we multiply:

So we use the same number required for the whole lawn, and multiply it times the hours