Final answer:
The exponential expression for multiplying the number 3 by itself four times is 3 to the fourth power, or 3^4.
Step-by-step explanation:
The exponential expression for the numerical expression 3·3·3·3 is 34. This is because you are multiplying the base number 3 by itself four times. Exponential notation is a way of representing repeated multiplication of the same factor. In this case, the base is 3, and the exponent is 4, indicating that the base is used as a factor four times.