I can try :)
Our numbers are in base 10. That means we use 10 digits 0,1,2,3,4,5,6,7,8 and 9
If I write this number
3658 it is the number $$3*10^3+6*10^2+5*10+8*1=3000+600+50+8$$
I can also write it like this $$3658_{10}$$ The little 10 means that it is base 10.
NOW
Mellie's numbers are not base 10
she has 332 base 4 and 212 base 3
$$\\332_4\\
$if I convert this to base 10 I get$\\
=3*4^2+3*4+2\\
=3*16+12+2\\
=48+12+2\\
=62\\\\\\
212_3\\
$if I convert this to base 10 I get$\\
=2*3^2+1*3+2*1\\
=2*9+3+2\\
=18+3+2\\
=23$$
The i just had to do the subtraction :)
Do you get it ?