How Is Net Energy Transferred in a Cyclic Thermodynamic Process?

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Homework Statement

A gas is taken through the cyclic process described by Figure P12.16.

http://www.webassign.net/sf/p12_16.gif

(a) Find the net energy transferred to the system by heat during one complete cycle.

(b) If the cycle is reversed -- that is, the process follows the path ACBA -- what is the net energy transferred by heat per cycle?

PV=[nR]T
[nR]=PV/T
W=-P(deltaV)What I have done so far:______P(kPa)--------V(m^3)------------U(J)--------------[nR]
A_____2x10^3--------- 6 --------------18x10^3 ----------43.96
B_____8x10^3----------10-------------120x10^3---------293.04
C_____2x10^3---------10---------------30x10^3-----------73.30
_________W(J)___________Q(J)___________deltaU(J)
A->B_____-8,000________110,000_________102,000
B->C______0__________-90,000___________-90,000
C->A_____8,000_________20,000__________-12,000

Wouldn't the net energy transferred to the system by heat be the sum of the Q values? I get 40,000J for this, but it seems to be wrong. Suggestions would be greatly appreciated.thanks

 

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I know its a bit tedious, but any suggestions?