Hi there!
Let's solve this problem step by step!

To find f(3) we must substitute x = 3 into the formula.

Now we use PEMDAS (Parenthesis, exponents, multiply, divide, add, subtract) to find our answer.
Work out the exponents inside the parenthesis first.

And finally multiply.

Hence, the answer is D. 64.
~ Hope this helps you!
21.12 is 25.6% of 82.5. I hope this helps. :)