Answer
a) Bonzo has the greater mass.
b) $\frac{m_{Bonzo}}{m_{Ender}}=1.67$
Work Step by Step
a) The principle of conservation of linear momentum states that $$m_1v_{f1}+m_2v_{f2}=m_1v_{01}+m_2v_{02}$$
Here, 2 enemies start off from stationary positions, so the initial total linear momentum equals $0$. In other words, $$m_1v_{f1}+m_2v_{f2}=0$$ $$m_1v_{f1}=-m_2v_{f2}$$
Since $v_{Ender}\gt v_{Bonzo}$ (magnitude of velocity), from the equation above, we can deduce that $m_{Ender}\lt m_{Bonzo}$, or Bonzo has the greater mass.
b) We have $$m_{Bonzo}v_{Bonzo}=-m_{Ender}v_{Ender}$$ $$\frac{m_{Bonzo}}{m_{Ender}}=-\frac{v_{Ender}}{v_{Bonzo}}=-\frac{(-2.5)}{1.5}=1.67$$
