Let total number of days they work together be D and the total cost of stitching 60 shirts and 30 pants be C.
Now, Ramdeen earns Rs. 15 per day and Ramsewak earns Rs. 20 per day.
∴ Total earnings of Ramdeen = Rs. D×15
∴ Total earnings of Ramsewak = Rs. D×20
∴ Total cost of stitching 60 shirts and 30 pants = C=D×20+D×15=D×35=35D
Also if Ramdeen stitches 6 shirts and 4 pants per day while Ram Sewak stiches 10 shirts and 4 pants per day,
Total shirts stitched = 60=(10+6)×D=16D
⟹D=154⟹D=4 days
Total pants stitched =30=(4+4)×D=8D
⟹D=154⟹D=4 days
Total cost for 4 days =35×4=140
Hence, the minimum number of days they work together is 4 and the total incurred cost is Rs. 140.