Final answer:
The formula to solve for m is m = d * V.
Step-by-step explanation:
The formula given is d = m/V, where d is the density of the substance, m is its mass, and V is its volume. To solve the formula for m, we can rearrange the equation. Multiply both sides of the equation by V to isolate m on one side, giving us m = d * V. Therefore, option B, m = d * V, is the correct answer.