tolong jawab no b, dengan cara please

b. n!/3!(n - 2)! = 5
{n (n - 1) (n - 2)!}/{3! (n- 2)!} = 5
{n(n - 1)}/3! = 5
n² - n = 5(3 x 2 x 1)
n² - n = 5 x 6
n² - n = 30
n² - n - 30 = 0
(n - 6)(n + 5) = 0
n = 6 V n = -5

jadi, yg memenuhi n = 6