The present system in Mathematics we use for representing numbers is a system which uses a base of 10.
We write 0 to 9 then next value we shift the digit from units to 10th place and write as 10. Thus we use only digits form 0 to 9, and place values for digits from right are
For less than 1 we use decimals and use place values from right to left as
Thus the system we use now is decimal system which has base 10.
ok so sam started with 0 and got -9 then he got 12 then the next known number is -8 so those three numbers together are -5 and the end result was -1 so -1 minus -5 is -4 therefore the anser is C