My question is in the pic

The first thing you need to know is the distance all the way around
the patio. The patio is in the shape of a circle, so the distance around
it is called the "circumference". You need the length of that.

Fortunately, you have a simple formula for the circumference of a circle:

     Circumference = (pi) times (the diameter of the circle) .

The diameter is  24.2  feet.

     Circumference = (pi) times (24.2 feet) = about 76 feet .

Now, all you need to do is figure out how many strings of lights
you need, for them to add up to 76 feet.

Each string of lights is  57 inches long.  You need to know how many
times you need 57 inches, to add up to 76 feet.

Well first of all, I hope you can see that you have to divide ... to find out
how many short pieces will make one long piece.

But there's another little wrinkle here:  The big distance is in feet,
and the short pieces are in inches, so you can't just go ahead and
divide 76 by 57. I mean, you could, but the answer wouldn't mean
anything.  Before you divide, both of your lengths need to be in
the same units, so you need to change one of them.  You have
a choice to make:  Either change the 76 feet into inches, or else
change the 57 inches into feet.  Either way works fine.

There are  12 inches  in one foot.

-- 76 feet = (76 x 12) = 912 inches.

(912 inches per patio)
                 divided by
                 (57 inches per light string) = 16 light strings per patio

or

-- 57 inches = (57/12) = 4.75 feet

(76 feet per patio)
             divided by
             (4.75 feet per light string) = 16 light strings per patio

See ?  Either way works fine.

Igot the answer of 15.8 years.