You can only add exponents if you are multiplying two of the same variable together. For example,
[tex]x^{12} \times x^4 = x^{16}[/tex]
You take them away if you are dividing.
[tex]x^{12} \div x^4 = x^{8}[/tex]
In a polynomial equation, you can add together two of the same variable if they have the same exponent
[tex]3x^4 + 7x^4 = 10x^4[/tex]
Or you can take them away in a similar fashion,
[tex]3x^4 - 7x^4 = -4x^4[/tex]
But you cannot add two (or more) different exponents,
[tex]6+4x+7x^2 = 6+4x+7x^2[/tex] (it does not get any simpler)
I hope this has answered your question, if not, leave a comment and I'll update the answer.
