[Chidori]

A piston performs a work of 210J on surroundings, while the cylinder it is placed in expands from 10 to 25L. At the same time, 45J of heat is transferred from the surroundings to the system. Against what pressure was the piston working?

I know I am supposed to use the equation W = -P deltaV

What I want to know is whether I should be adding 45J to the existing 210J or subtracting from it etc?

[iceman]

this question is worded weird.  it can be either way. "A piston performs a work of 210J on surroundings." could mean that the 210J includes or doesn't include the 45J from the surroundings.

But i think it DOESN'T include the 45J from the surroundings. so the 210J + 45J = total J in the system