$\begin{array}{r}2.84 \\ \times 3.9 \\ \hline\end{array}$

Step 1 ：This is a simple multiplication problem. We need to multiply 2.84 by 3.9.

Step 2 ：The result of the multiplication is 11.075999999999999, but this is a floating point number and it's not exactly accurate due to the way floating point numbers are represented in computers. We can round this number to a reasonable number of decimal places to get a more accurate answer.

Step 3 ：Final Answer: \(\boxed{11.08}\)