Thermodynamics problem- isobaric process

[mrdith007]

Homework Statement

One mole of an ideal monatomic gas is taken through the cycle ABCA shown schematically
in the diagram. State A has volume 0.0208 m³ and pressure 1.22 × 10 ⁵ Pa, and state C has volume 0.0524 m³ Process CA lies along the 305 ±1 K isotherm. The molar heat capacities for the gas are 20.8 J/mol · K and 12.5 J/mol · K.

Determine the heat Q_ab added to the gas during process AB.
Answer in units of J

I have attached an image with the graph. I am not sure if it is necessary. I got the correct answer to the first question (the new temp = 768.365 K)

Homework Equations

W = p\DeltaV
Q = \DeltaU + W

The Attempt at a Solution

I do not know how to calculate the U, which I think I need

 

[gamma5772]

\Delta U = C_V \Delta T for an ideal gas.