(A)Two point charges `q_1` and `q_2` are kept r distance apart in a uniform external electric field `vecE`. Find the amount of work done in assembling this system of charges. (B) A cube of side 20 cm is kept in a region as shown in the figure. An electric field `vecE` exists in the region such that the potential at a point is given by `V = 10x + 5`, where V is in volt and x is in m. Find the electric field `vecE` and (ii) total electric flux through the cube.