Okay, first, given the equation, we need to find out what the radius of the circle is. Let us state the general equation of a circle:

Where

is the centre of the circle. In this case, we don't need to know the centre. Just the radius.
Let us start by converting the equation into standard for, which I typed above. Divide both sides by 81.

Great! We now know the radius of the circle. It is

because it is the bottom fraction. Now we know that the radius is 9.
So now lets input this into the area of circle formula:
Now we insert our radius.
You can convert that into a decimal if you wish.
Hope this helped!
~Cam943, Moderator
We can follow the following steps to make an equation and solve it.
Step 1:
five less than 13 means we have to subtract 5 from 13
so it becomes 13-5
Step 2:
A number y is five less than thirteen.
Now in algebraic expressions, "is" stands for "="
So we have:

Step 3:
Solving the equation to find y.

Subtracting 5 from 13, we get :
y=8
Answer:
For the given equation the solution is y=8.
Practice, practice & practice.
You paid $4.76 total for 7 notebooks. To figure out how much each individual notebook cost, you divide the total cost by the number of things you bought, so
Cost of One Notebook = Total Cost of Notebooks / Number of Notebooks = $4.76 / 7 = $0.68
This is the unit rate.
To buy three notebooks, you just calculate the total cost of three notebooks at this price point, so
Cost of Three Notebooks = Cost of One Notebook * 3 Notebo0ks = $0.68 * 3 = $2.04