Find the 4th proportional to 4 , 16 and 7 ,

Lat the 4th proportional = N
Then, 4 : 16 : : 7 : N
⇒ 4/16 = 7/N
⇒ 4N = 7 x 16
∴ N = (7 x 16)/4 = 7 x 4 = 28