In general, the mean value of a histogram is given by the formula below
[tex]\begin{gathered} mean=\sum_i\frac{m_in_i}{N} \\ m_i\rightarrow\text{ midpoint of the ith interval} \\ n_i\rightarrow\text{ frequency of the ith interval} \\ N\rightarrow\text{ Total sample size} \end{gathered}[/tex]Thus, in our case,
[tex]\begin{gathered} mean=\frac{1}{3+7+13+20+7+6+2+2}(3*104.5+7*114.5+13*124.5+20*134.5+7*144.5+6*154.5+2*164.5+2*174.5) \\ \Rightarrow mean=\frac{1}{60}(8040)=134 \end{gathered}[/tex]As for the median of a histogram, order the values of the data set from least to greatest, as shown below
[tex]\begin{gathered} 1st,1st,1st,2nd,2nd,...,3rd,3rd,...,7th,7th,8th,8th \\ Where \\ 1st\rightarrow indicates\text{ an element in the first interval \lparen100-109\rparen} \\ 2nd\rightarrow\text{ indicates an element in the second interval \lparen110-119\rparen} \\ ... \end{gathered}[/tex]Thus, the median of the distribution is
[tex]\begin{gathered} 3+7+13+20+7+6+2+2=60 \\ \Rightarrow median=\frac{29th\text{ }value+30th\text{ }value}{2}=130-139\text{ class} \end{gathered}[/tex]