Molar Specific Heat Homework: Calculating Change in Internal Energy

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Homework Statement

Let 25.2 J of heat be added to a particular ideal gas. As a result, its volume changes from 46.0 to 101.2 cm3 while the pressure remains constant at 1.0 atm. By how much did the internal energy of the gas change?
19.6 J is the answer which i understand how to get the next question is

What is the molar specific heat at constant pressure?
I have tried so many different ways. I don't know if I am doing conversions wrong or not setting it up right. I am pretty sure all my conversions are right.

Homework Equations

The Attempt at a Solution

 

[Indy2424]

I feel like there is something missing for the problem. Please help!