Idon't understand these following questions, can someone me?
1) find the work done by a 25 n force applied for 6 meters
2) calculate the potential energy of a 5 kg object sitting on a 3 m ledge
3) a rock is at the top of a 20 meter tall hill, the rock has a mass of 10 kg. how much potential energy does it have?

These questions are testing to see if you know
the formulas for work and potential energy ... or
if you know where to find them when you need them.

1).  The formula for work is:

                       Work = (force) x (distance) .

In this question:  Work = (25 N) x (6 m) = 160 joules .


The formula for potential energy is

                   PE  = (mass) x (gravity) x (height) .

On Earth, gravity = 9.8 m/s² 

This information gives you both of the other questions.

#2).  PE  = (mass) x (gravity) x (height)

               = (5 kg) x (9.8 m/s²) x (3m) =  147 joules

#3).  PE  = (mass) x (gravity) x (height)

               = (10 kg) x (9.8 m/s²) x (20 m) =  1,960 joules

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current