What is the value of d if 3d = 21?

To determine the value of d in the equation 3d = 21, you can isolate d by performing the inverse operation. In this case, you need to divide both sides of the equation by 3.

Doing the calculation:

d = 21 ÷ 3

When you divide 21 by 3, you arrive at 7. Thus, d equals 7.

This reasoning confirms that the correct answer is 7, as it directly results from solving the equation correctly. Understanding how to rearrange an equation and perform division is essential in algebra, leading to accurate solutions.