Force on a moving charge — practice question

A sphere with mass $1.6 \times 10^{-10}\,\text{kg}$ carries a charge of $+0.27\,\text{nC}$. It lies in a uniform electric field acting vertically upwards, as illustrated by the side view in Fig. 2.1. The electric force on the sphere keeps it at one fixed vertical level in a horizontal plane. A uniform magnetic field is present in the same region as the electric field. The sphere travels at $0.78\,\text{m s}^{-1}$ in the horizontal plane. This magnetic field makes the sphere follow a circular path of radius $3.4\,\text{m}$, as shown in the view from above in Fig. 2.2.