Two tiny spheres of mass m = 6.80 g carry charges of equal magnitude, 72.0 C, but of opposite signs. They are
tied to the same ceiling hook by light (effectively massless) strings L = 0.530 m. When a horizontal uniform
electric field E that is directed to the left is introduced, the spheres hang at rest with the angle ® between the strings equal to 50.0., as shown in the figure.

Which ball (the one on the right or the one on the left) has a positive charge?