What is the sum of the possible units digits of a perfect square written in base 6?
just look at the last digit squared.
0^0=0
1^2=1
2^2=4
3^2=9 no that is not possible 9=6+3 so 3
4^2=16 16=2*6+4 so 4
5^2=
I will leave the last one to you to do.