Answer:
Leg Raises ⇒ Abdominals
The raising of and return of the leg motion contracts and relaxes the abdominal muscles thereby exercising it.
Pushdowns ⇒ Triceps
The triceps are activated during motions that require the arms to push so pushdowns work the triceps.
Bench Press ⇒ Pectorals
This is one of the most effective and popular exercise for the pectoral muscles of the chest. It is also very effective for the triceps.
Machine Back Press ⇒ Shoulders
Using this machine activates the shoulders. As the shoulders are not very large muscles, care must be taken when using this so as not to overtax the shoulders.