multiply in the indicated base the base is 9
503
x 67
¬¬¬¬¬¬¬¬¬¬¬¬
If you have lots of these, them make yourself a base 9 multiplication table and an addition table.
If you only have one, I would change the numbers to base 10, do the arithmetic in base 10, then convert back.
e.g. 5039 = 5(9^2) + 0(9) + 3 = 408
67 = 6(9) + 7 = 61
408x61 = 24888
24888 = 3(9^4) + 7(9^3) + 1(9^2) + 2(9) + 3
= 371239
(Editorial: Tell your teacher to stop teaching "silly" math like this and concentrate on real mathematics.
Unless you are working in base 2, or base 8 --> 1 byte, or base 16 which is used in actual coding of computer software, all this other stuff is no better in teaching you mathematics than doing cross-word puzzles. )