we do not have Ca, you may state it in terms of another constant, To obtain the exact solution, you must apply Bernoulli's eqn solution steps to the eqn which you gave in the Fig. That eqn is just a function of Cb depending on Then, you'll be got Cb as a function of. Once you did it, you must take derivation of Cb depending on t to obtain max Cb, At this point you must also make an assumption by taking in consideration of what? This is the key.

Find k2? D Ab C Bu k=? ki. 5.65 x152 in Max & Conc. is amad -da dt ICA - dC ? 2 YA dt - dla akce dt