You can find the answer by adding all the values and dividing by the number of values (in this case 4)
So the answer is
$${\frac{\left({\mathtt{4.5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3.5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{5.5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2.9}}\right)}{{\mathtt{4}}}} = {\frac{{\mathtt{41}}}{{\mathtt{10}}}} = {\mathtt{4.1}}$$
So your answer is $4.10
Reinout 