Final answer:
The expression 13.8 + x evaluated for x=2.31 results in the sum of 16.11.
Step-by-step explanation:
To evaluate the expression 13.8 + x for x=2.31, you simply add the value of x to 13.8. So, the calculation will be as follows:
13.8 + 2.31 = 16.11
Therefore, the evaluated expression equals 16.11.