What is the solution to 7x = 21?

To find the solution to the equation (7x = 21), you want to isolate the variable (x). This can be done by dividing both sides of the equation by 7. Doing this step-by-step looks like this:

1. Start with the equation: (7x = 21).
2. Divide both sides of the equation by 7:

[ \frac{7x}{7} = \frac{21}{7} ]

3. Simplifying both sides gives:

[ x = 3 ]

This means the solution to the equation (7x = 21) is (x = 3). Therefore, option B is the correct answer, as it correctly reflects the value of (x) that satisfies the original equation.