Factorise n(squared) - 7n + 12
explain your answer

The best way to improve your skill factoring this trinomials is just to practice and practice again. 
So basically we need 2 numbers that multiply to 12 and that add up to -7. Using some intuition and some guess and check, we learn that the 2 numbers are -4 and -3. Putting them into 2 binomials, we get 

(n-4)(n-3)

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