4⁶ · 4⁷ = 4¹³
Since these two powers have the same base of 4, you can multiply
them together by simply adding their exponents to get 4¹³.
This idea is called the product rule.
A common mistake in this problem would be to multiply
the bases together and give an answer of 16¹³.
It's important to understand however that the 4's in this problem can't
be multiplied together because they're not coefficients, they're bases.
When applying your exponent rules, your base will never change.