In which of the following would you multiply both sides of the equation by n? A) Solve for m/n = p for m. B) Solve m - n = p for m. C) Solve mn = p for m. D) Solve m + n = p for m.

A multiply operation is designed to "undo" a divide operation. The problem statement with a "divided by n" in it is the problem statement ...
  A) m/n = p After multiplying by n, you would have
  m = n*p    which is the desired solution for that problem statement.
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  B) m - n = p
  m = p + n    (add n to both sides)

  C) mn = p
  m = p/n    (divide both sides by n)

  D) m + n = p
  m = p - n    (subtract n from both sides)

If you master these solutions, you are well on your way to solving any algebra problem involving linear equations.