for 1's complement
a)A=101010=-21 and B=+34 maximum range of number in 1's complement number for 6 bit is -31 to +31 so A+B can't overflow.
b) A-B =-55 which is out of range so overflow occur.
for 2's complement range =-32 to +31
a)A=101010=-22 and B=+35
A+B overflow can't occur.
b)A-B =-57 overflow occur