My TI-84 Plus Silver Edition is giving regular math problems (.064/160000) an answer involving an E (4E-7) and I'm not sure how to change it.

There is no such thing as a TI89 Plus Silver Edition.

If you mean the TI-89 or TI-89 Titanium, press diamond / (the diamond key below the 2ND key, then the divide key).

If you mean the TI-83 Plus Silver Edition or the TI-84 Plus Silver Edition, press MATH left-arrow 4 .

Enter the numerator and denominator then press Math ToFrac

Press MATH ENTER to invoke the >Frac command.

Press MATH ENTER to invoke the >Frac command.

There are no such buttons, You'll find the lcm (least common multiple) and gcd (greatest common divisor) functions in the MATH NUM menu. Press MATH, right-arrow, and select the desired function.

There isn't one. If you want to convert a value from decimal to fraction, use the >Frac function (press MATH 1). If you want to enter a fraction, simply enter the numerator, divide, then the denominator.

For example, to calculate 1/4 + 1/3, press
( 1 / 4 ) + ( 1 / 3 ) MATH 1 ENTER
and you'll see 7/12.

Press 4 then press math. Select #5. You'll be back at the home screen now type 90 and press enter. You can use this for any root.

The TI 83, 84 series can not set up the answers as fraction. What you have to do to get fraction answer is to go to math,1. the very first selection which is ->frac. What will change your answers into fractions 

Press the MATH key to display the Math menu.

>Frac converts a decimal value to a fraction.
>Dec converts a fraction to a decimal value.

Enter the fraction for example: enter 8/12.
The answer will be .666666
Then click Math (which is located under the Alpha button).
Click the ->Frac button (the first one).
It should come up as Ans->Frac.
Click Enter.
It should now read 2/3 which is 8/12 reduced.
Note: I have a TI-84 Plus Silver Edition, and the TI-84 Plus might not have this function, but that is how I do it on my TI-84 Plus Silver Edition