A residence time distribution analysis was performed with the trace substance in a reactor. Accordingly, the exit

the concentration of the substance leaving traces in the current is linear within the first $5$ minutes, starting from $0$ mg$/$L

it was observed that it increased to $15$ mg$/$L and linearly decreased to $0$ mg$/$L within the next $10$ minutes. This

according to the information, please answer the following questions.

a$)$ C$($t$)-$draw the time graph.

b$)$ Calculate the variance according to the average residence time $($tm$)$ of $6\mathrm{.}7$ minutes.