Question

How would you factor c(m - n) + d(m - n)?

A)   cd(m - n)

B)   (c - d)((m - n)

C)   (c + d)(m - n)

D)   (c - d)(m + n)

Answer 1

the answer is (c+b)(m-n) because m-n is on both sides of the + and so they can be added together making it easier to figure out if you have the numbers to replace the variables. 

Answer 2

remember
ab+ac=a(b+c)
if we reverse it
ba+ca=a(b+c)
so
c(m-n)+d(m-n)=(m-n)(c+d)
(c+d)(m-n)

C is answer