12 base 5 divide by 4021 base 5
I would change them back to base 10
12 base 5 = 7 base 10
4021 base 5 = 511 base 10
so 12(b5)/4021(b5)
= 7/511
= 1/73
= 1/243 (b5)
these kind of questions became popular back in the 60's when the Soviet launched Sputnik and the US panicked, thinking they were behind in the maths and sciences and introduced "New Math"
Most jurisdictions have abandoned such fruitless kind of math.
The only useful arithmetic in different bases would be base 2 (binary) because computers work in base 2,
base 8 (one byte is 8 bits) or
the hexadecimal number system of base 16