Total sum of the data set = 15
Explanations:The mean of a set of data is given by the formula:
[tex]\begin{gathered} \text{Mean = }\frac{\sum ^{}_{}x}{n} \\ \text{Where n is the number of items} \end{gathered}[/tex]There are three pieces of data here:
n = 3
[tex]\begin{gathered} \text{Mean = }\frac{x_1+x_2+x_3}{3} \\ \operatorname{mean}\text{ = 5} \\ x_1=\text{ 4} \\ x_2=\text{ ?} \\ x_3=\text{ 6} \end{gathered}[/tex][tex]\begin{gathered} 5\text{ = }\frac{4+x_2+6}{3} \\ 5\times3=4+6+x_2 \\ 15=10+x_2 \\ 15-10=x_2 \\ x_2=\text{ 5} \end{gathered}[/tex][tex]\begin{gathered} \text{Total sum of the data = x}_1+x_2+x_3 \\ \text{Total sum of the data = 4 + 5 + 6} \\ \text{Total sum of the data = 15} \end{gathered}[/tex]