I.Given : 75 is a factor of n.
⇒ n is a multiple of 75.
e.g. 75, 150, 225, ....... and so on.
∴ I alone is not sufficient.
II. Given : 45 is a factor of n.
⇒ n is a multiple of 45.
e.g. 45, 90, 135, 180, 225, ....... and so on.
∴ II alone is not sufficient.
I & II.
n is a multiple of both 75 and 45.
LCM (75, 45) = 225
⇒ n is a multiple of 225.
e.g. 225, 450, 675, .......
Hence, n is divisible by 225
∴ I & II together are sufficient