Cost of one radio set $$=$$Rs. $$1200$$
Cost of $$40$$ radio sets $$=1200\times 40$$ Rs. $$48000$$
Money with Merchant$$=$$Rs. $$78,592$$
Money spent$$=$$Rs. $$48,000$$
Money left $$=78592-48000$$
$$78592$$
$$-48000$$
___________
$$30592$$
___________
Therefore, Rs. $$30,592$$ will remain with her after the purchase.