A watch was sold at a loss of 10%. If it was sold for Rs.140 more, there would have been a gain of 4%. What is the cost price ?

Let the cost price of the watch be x.
It was sold for 10% loss that is 90x/100

If it was sold for 140 more, the price would be 90x/100 + 140 and this would be 4% gain which is 104x/100

So, 104x/100 = 90x/100 + 140
Multiply through by 100, we have
104x =90x + 14000
Subtract 90x from both sides, we have
14x = 14000
Divide both sides by 14, we have
x = 1000
So, the cost price is 1000