Let the four numbers be m, n, o, p.

From the given data,

Average of the first three out of four numbers is 18

⇒ (m + n + o) /3 = 18

⇒ Sum of the first three numbers (m + n + o) = 54       ----(1)

Also given that average of the last three numbers = 14

⇒ (n + o + p)/3 = 14

⇒ Sum of the last three numbers (n + o + p) = 42       ---- (2)

Subtract equation (2) from equation (1), we get

⇒ m - p = 12       ----(3)

Also given that sum of the first and last number = 16

⇒ m + p = 16      ----(4)

Subtract equation (4) from equation (3), we get

⇒ -2p = -4

∴ p = 2