Old Scenario:
$\text{Total Cost} = \text{₹}13200$
$\text{Working Hours(per day)} = t_d$
$\text{Total Days of Work} = d$
$\text{Total Working Hours} = \text{Working Hours(per day)} \times \text{Total Days of Work} = t_d \times d$
$\text{Labour Wages(per day)} = w_d$
$\text{Total Cost} = \text{Total Days of Work} \times \text{Labour Wages(per day)} = \text{₹}13200$
$\therefore d \times w_d = \text{₹}13200$
New Scenario:
$\text{Labour Wages(per day)} = w_d \times (1 + 1/5) = \frac{6}{5} w_d$
$\text{Working Hours(per day)} = t_d \times (1 - 1/24) =\frac{23}{24} t_d$
Assuming, NO change in worker efficiency, the $\underline{\text{Total Working Hours}}$ will remain constant.
$\therefore$ Since the working hours per day have decreased, The number of working days will increase.
$\therefore \text{Total Days of Work} = \frac{\text{Total Working Hours}}{\text{Working Hours(per day)}} = (t_d \times d)/(\frac{23}{24}\times t_d) = \frac{24}{23} d$
$\therefore \text{Total Cost} = \text{Total Days of Work} \times \text{Labour Wages(per day)} = (\frac{24}{23} d) \times (\frac{6}{5} w_d)$
$= \frac{6 \times 24}{5 \times 23}(d \times w_d) = \frac{6 \times 24}{5 \times 23} \times 13200 = 16528.69$