To factor this is expression, one simple way to do this is to place brackets surrounding each set of 2 terms. Do brackets around m^2 and 8mn and brackets around -3mn - 24n^2.
Then solve for the common factor in each bracket group.
m(m + 8n) - 3n(m + 8n)
(m-3n)(m + 8n) is the answer.
