By selling a bouquet for Rs 322, a florist gains 15%.

SP of the bouquet = Rs 322

Gain percentage = 15%

$\mathrm{CP}$ of the bouquet $=\left(\frac{100}{100+\text { gain } \%}\right) \times \mathrm{SP}$

$=\operatorname{Rs}\left(\frac{100}{100+15}\right) \times 322$

$=\mathrm{Rs} \frac{100}{115} \times 322$

$=$ Rs 280

Now, CP = Rs 128 and desired gain percentage $=25 \%$

$\therefore$ Desired SP $=\left(\frac{100+\text { gain } \%}{100}\right) \times \mathrm{CP}$

$=$ Rs $\frac{125}{100} \times 280$

$=$ Rs 350

​Hence, the selling price to obtain the desired gain must be Rs 350.