Question 516243
Here are the steps, and you'll need to know that a^2 - b^2 = (a + b)(a - b)
3r - 3k + 3r^2 - 3k^2
[3 comes out of each difference]
3(r-k) + 3(r^2 - k^2)
[apply: a^2 - b^2 = (a + b)(a - b)]
3(r-k) + 3(r + k)(r - k) 
[one more thing to factor: 3(r - k)]
(3(r - k))(1 + (r + k))
[some parentheses were only included for clarification, and aren't needed]
3(r - k)(1 + r + k)


m^2 - p^2 + 2m + 2p 
[apply: a^2 - b^2 = (a + b)(a - b)]
(m + p)(m - p) + 2(m + p) 
[factor out "(m + p)"]
(m + p)(m - p + 2)