$4 \times 37 + 11 \times 41+ 161 = 760$ kilograms in total.  $760 \div (4 + 11 + 5) = 38$ kg. 
The average weight of $4$ students in Class $A$ is $37$ kilograms. The average weight of $11$ students in Class $B$ is $41$ kilograms. The total weight of $5$ students in Class $C$ is $161$ kilograms. What is the average weight of the students in the $3$ classes? 
Options:
(a) $36$ kilograms 
(b) $38$ kilograms 
(c) $40$ kilograms 
(d) $43$ kilograms 