Let C be the original capital. After losing in the first operation what remained was 0.65C.
After losing 40% of this in the second operation he is left with 60% of this remainder=0.60×0.65C=0.39C=15600.
So C=15600/0.39=40,000.
CHECK
1st operation: he lost 35% of 40,000=14,000, leaving 26,000.
2nd operation: he lost 40% of 26000=10,400, leaving 15,600.