The value of δe for a system that performs 168 kj of work on its surroundings and loses 79 kj of heat is kj.

- 247 kJ

Explanation:

The formula you need to now is very simple:

ΔE = Q + W

This basically means that in order to calculate ΔE, you need to now the heat Q that the system loses or gains, and the work W that it perfoms or receives.

The system that we have loses heat, so Q is negative, and performs a work, which consumes energy, therefore W is also negative. So, in conclusion, we have:

ΔE = Q + W = -79 kJ - 168kJ = - 247 kJ.

The system loses 247 kJ of energy.