You have posted 2 separate questions here.  Please, next time, separate them with a blank line:
<span>A circle has an area of 81 3.14 units . what is the diameter in terms of 3.14?
I'd prefer you write this as 
"</span><span>A circle has an area of 81 pi units . what is the diameter in terms of pi?
Area of a circle = A = pi*r^2.  Note that r= diameter / 2.  Here, the area is 81 pi square units, or 9^2 * pi square units, which means that the radius is 9 units.  The diameter is then 2(9 units) = 18 units.
Your second question, separated from the first, is:
"</span><span>a circle has an area of 81 Pi square units what is the diameter of the circle?"
</span><span>
Use the following formula or formulas:  d = 2*r; A = pi*r^2; A = pi*(d/2)^2.  Find r first, and then find d.
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Answer:
 $11.20
Step-by-step explanation:
The regular price of the T-Shirt is $14 dollars. The discount is 20% off.
20 percent of 14:
14 * 0.2 = 2.80
You would save $2.80. 
14 - 2.80 = 11.20
The discount price should be $11.20.
Hope this helps.
 
        
             
        
        
        
Answer:
132 ft squared
Step-by-step explanation:
One way is to divide the shape into a rectangle and a triangle, by drawing a vertical line. 
This gives a rectangle that is 9 by 11, so has area 99.
The triangle has a base of 11 and height of 15 - 9 = 6. 
So the area of the triangle = 1/2 x b x h = 1/2 x 11 x 6 = 33
So the total area is 99 + 33 = 132. 
 
        
             
        
        
        
Please mark Brainliest
The answer is 17. 72
Step by step 
0.02x^2 = 6.28
x^2 = 6.28 / 0.02
x^2 = 314
x= square root of 314
x = 17. 72
        
                    
             
        
        
        
The unites to measure the volume of an object is what ever units you’re using cubed