Complex sentence: Main power was from four Viking 5 motors each producing 667 kN of thrust; the second stage had a single Viking motor; and the third stage had an HM7 liquid oxygen/liquid hydrogen motor.
Split into simpler sentences: Main power was from four Viking 5 motors each producing 667 kN of thrust. The second stage had a single Viking motor, and the third stage had an HM7 liquid oxygen/liquid hydrogen motor.