In order to meet $B$ at point $M_{3}$, $A$ travels to $M_{1}$ first, then $M_{2}$ & then $M_{3}$.
$\color{green}{\text{So, Total distances travelled by}}$ $\color{red}{A}$ $\color{green}{\text{when it meets with}}$ $\color{red}{B}$ $\color{green}{\text{at point}}$ $\color{red}{M_{3}}$ $\color{green}{is}$ $\color{blue}{33+11+33=77\hspace{0.1cm}km}$
$\big[\color{orange}{∵M_0\rightarrow M_1 =M_0\rightarrow M_3+M_3\rightarrow M_2+M_2\rightarrow M_1 = 11+11+11\hspace{0.1cm}km = 33\hspace{0.1cm}km}\big]$
&$\big[\color{orange}{M_1\rightarrow M_2 =11\hspace{0.1cm}km}\big]$
&$\big[\color{orange}{∵M_2\rightarrow M_3 =M_2\rightarrow M_1+M_1\rightarrow M_0+M_0\rightarrow M_3 = 11+11+11\hspace{0.1cm}km = 33\hspace{0.1cm}km}\big]$