Factor by grouping. \( 15 r m+20 r-3 p m-4 p \) \( \square \)

To factor by grouping, first group the terms: \((15rm + 20r) + (-3pm - 4p)\). Now, factor out the common factors from each group: \(5r(3m + 4) - p(3m + 4)\). Notice that both groups contain the common binomial \((3m + 4)\): \((5r - p)(3m + 4)\). And there you have it! The expression is factored as \((5r - p)(3m + 4)\).