Use the formula x+y-(x*y/100) where x and y are the successive discount percentages. Here they are 15% and 10%. So by using the formula, we obtain

15+10-15*10/100= 23. 5. Here 23. 5 is the new discount%

Now 23. 5% of 4000 is 940 and the new price is 4000-940=3060 . Also with another discount of 5% on 3060 i.e 153, final price is 3060-153= 2907