An electrical field deflects beams of charged particles. The deflection angle of a particle is proportional to its charge / mass ratio. In one experiment, protons are deflected through an angle of $+15^{\circ}$. In a separate experiment carried out under identical conditions, $^2_1\text{H}^+$ ions are deflected through an angle of $Y^{\circ}$. What is the value of $Y$?
- A$-30.0$
- B$-7.5$
- C$+7.5$
- D$+30.0$