It can be modeled by an exponential function, f(x) is divided by 3 each time x increases by 1.
This means that the base of the exponential function is 1/3, and since the value of f(x) when x=0 is 81, 
Answer:
-5 or 5 depending on how you write the simplified form
Step-by-step explanation:

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The applicable rules of exponents are ...
(a^b)(a^c) = a^(b+c)
1/a^b = a^-b
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Some folks like their simplified form to contain only positive exponents. Other folks avoid unnecessary fractions. Choose the form that satisfies your grader.
Answer:
Imagine an easier version of this problem: You have a board 5 feet long that you must cut (divide, right?) into two equal parts. It is probably clear to you that you simply divide the length (5) by the number of parts you're dividing it into (2) to obtain the length of each piece (2.5 feet).
Use the same method for your problem 5 feet divided by 6 is 0.83 feet per piece.
We do not ordinarily divide feet into decimal portions, but instead into inches. Since an inch is 1/12 of a foot, you could simply say 5/6 = how many twelfths? or 5/6 = n/12 Solve this by inspection or by cross multiplying 5 times 12 equals n times 6. So n must equal 10, and your pieces of board are each 10 inches long.
Answer:
x = 51
Step-by-step explanation:
(x-3) /4 = 12
Multiply each side by 4
(x-3) /4 *4 = 12*4
x-3 = 48
Add 3 to each side
x-3+3 = 48+3
x = 51