Always vibe Alone

Do levers always act alone, or do they act with other machines? Give an example of a lever working with another simple machine.

Cartilage fish are always marine and are always ammonotelic/Ureotetic.

G and H can do a work in 30 days .If H alone can do it in 50 days ,then G alone can do it in ___ days .

If Rohit alone can complete one-fourth of a work in 32 days, then in how many days Rohit alone can complete the whole work?