The expression that would use the product rule, adding the exponents, is:
3³ ⋅ 3
When you multiply terms with the same base, you add their exponents. In this case, 3 can be rewritten as 3¹, so:
3³ ⋅ 3¹ = 3^(3+1) = 3⁴
This demonstrates the use of the product rule for exponents.