To solve the equation \((2,3 + x) : 2 = 3,1\), let's first clarify the notation. The colon (:) typically represents division. So, the equation can be rewritten as:

\[
\frac{2.3 + x}{2} = 3.1
\]

To solve for \(x\), follow these steps:

1. Multiply both sides of the equation by 2 to eliminate the fraction:

\[
2.3 + x = 3.1 \times 2
\]

2. Calculate \(3.1 \times 2\):

\[
3.1 \times 2 = 6.2
\]

So the equation now is:

\[
2.3 + x = 6.2
\]

3. Subtract 2.3 from both sides to solve for \(x\):

\[
x = 6.2 - 2.3
\]

4. Perform the subtraction:

\[
x = 3.9
\]

Therefore, the solution to the equation is:

\[
x = 3.9
\]