If he spent the 40% it means the remaining persent is 60% so the answer in the question "how much percent of his salary was left?" is 60%
Instead of telling you the final answer in the last question, I will just guide you how to solve.
60% = 6300
40% = ?
100% = ?
to get the 40%, divide 6300 to 3 then multiply to 2 (this is because 60/3=20 x 2=40)
the answer in 100% will be your final answer. To get that, add 6300 and the answer you got in 40%