Hi everyone~is me again...I don't understand what is the meaning of 300 of B727-300.Is it mean that the aircraft has 3 enignes??But,where is the other one besides the two engines at each both wings?Can someone explain to me, please.Thank You!

The B727-300 never went into production. It was supposed to be a stretched version of the B727-200 with JT8D-200s engines like the MD80. modified wing leading edge, and four-wheel main gear trucks. It got cancelled because UAL declined to order them.