Which is the best example of forces acting in the same direction?
a boy lifting his chest off the ground during a pushup
two football players pushing a tackling sled
a person pulling out a garden hose from its reel
two dogs playing tug-of-war with a rope

Aproduction line at v. j. sugumaran's machine shop has three stations. the first station can process a unit in 7 minutes. the second station has two identical machines, each of which can process a unit in 16 minutes (each unit only needs to be processed on one of the two machines). the third station can process a unit in 10 minutes. ▼ is the bottleneck station, with a bottleneck time of nothing minutes per unit (enter your response as a whole number).