Sphere a has a charge of +2 x 10 to the power of -6 coulomb and is brought into contact with a similar sphere, b which has a charge of -4 x 10 to the power of -6 coulomb. after it is separated from sphere b, sphere a will have a charge of
a) +2 x 10 to the -6 power c
b) -1 x 10 to the -6 power c
c) +6 x 10 to the -6 power c
d) -2 x 10 to the -6 power c

* explain as i'm lost, you! : )