Answer
(a) The charge ends up on sphere C is $+1.5q$
(b) The total charge on the three spheres before they are allowed to touch each other is $+4q$
(c) The total charge on the three spheres after they they have touched should be $+4q$
Work Step by Step
(a) First, the sphere A is touched to sphere B, the resultant charge becomes $(+5q-q)=+4q$
After their separation, the charge to each sphere A and B becomes $(+4q\div2)=+2q$
Second, the sphere C is touched to sphere A, the resultant charge becomes $(+2q+0)=+2q$
After their separation, the charge to each sphere C and A becomes $(+2q\div2)=+q$
Third, the sphere C is touched to sphere B, the resultant charge becomes $(+q+2q)=+3q$
After their separation, the charge to each sphere C and B becomes $(+3q\div2)=+1.5q$
Thus the charge ends up on sphere C is $+1.5q$
(b) The total charge on the three spheres before they are allowed to touch each other $=(+5q-q+0)=+4q$
(c) According to law of conservation of electric charges, the total charge on the three spheres after they they have touched should be $+4q$
