What is the cube of 7?

The cube of a number is calculated by multiplying that number by itself twice. In this case, to find the cube of 7, you would perform the calculation as follows:

7 x 7 x 7 = 49 x 7 = 343.

Therefore, the cube of 7 is 343, which confirms that the correct answer is indeed the first choice. This value is derived from understanding that cubing a number involves three instances of the number being multiplied together. The other choices either represent incorrect calculations or different mathematical operations, such as squaring or multiplying by unrelated numbers.