Lubna Afroz, I think the operating frequency of the NMR instrument is 400 Hz. The following answer is based on that consideration.

For the quartet peak centred at 8.125 ppm, the coupling constant is 20.53 Hz

For the triplet peak centred at 7.325 ppm, the coupling constant is 31.2 Hz

For the quartet peak centred at 7.158 ppm, the coupling constant is 12.93 Hz

For detailed calculations, please check the image.

Swapnamoy Ganguly Thank you so much for the answer sir. The calculation is so clear and precise.

Dear Lubna Afroz a conclusive analysis and answer to your question can only be given if the splitting pattern of your signals is clearly perceptible. This is not the case with your illustration. Swapnamoy Ganguly , I do not agree with your analysis for two reasons: (1) you cannot be sure that the signals are "triplets" or "quartets" (I doubt about that) and hence the calculation is questionable; (2) coupling constants larger than 20 Hz are very rare, not to say unlikely for organic compounds.

Moreover, applying a line broadenig factor of 1 Hz is not really helpful for most proton spectra, and the integral labels look very strange to me (as there are four regions of relative intensity 2 but only three peaks groups of appropriate size). Please check everything.