Answer:
The weight required on the piston equals 420 Newtons.
Step-by-step explanation:
from the principle of transmission of pressure in a hydraulic lift we have

where
'F' is the force that acts on the piston
'A' is the area of the piston.
Since the force in the question is 21000 Newtons thus upon putting the values in the above equation we get

Solving for
we get
