The standard equation of a circle is:

where (h,k) is the center and r is the radius.
We need to make an equation of a circle, whose center is (11,-5) with any radius. Therefore, substitute the value.

The bolded part is your answer. Since the radius is not given, we can put any value.
Answer:
The unit price of brant A and brand B is 0.1311 and 0.1704 and brand A would be better
Step-by-step explanation:
The computation of the unit price for each brand is shown below:
For brand A, the unit price is
= 2.36 ÷ 18 pencils
= 0.1311
For Brand b, the unit price is
= 4.09 ÷ 24
= 0.1704
So here as we can see that brand A would be better as it has less cost as compared with brand B