Answer:
(n-3y)(m-3x)
Step-by-step explanation:
group the first 2 terms and the last two terms:
(mn-3my) and (-3nx+9xy)
factor out the greatest common factor from each group:
m(n-3y) and -3x(n-3y)
the terms in each of the bracket should be the same so you put them in the first bracket:
(n-3y)
then times this by the terms on the outside of the two brackets:
(n-3y)(m-3x)
hope this helps :)