$${\begin{align*} v_{fi} &= \frac{m_1 - m_2}{m_1 + m_2} v_{1i} = \\&= \mathrm{\frac{0,030\, kg - 0,075\, kg}{0,030\, kg + 0,075\, kg}(1,252\, m/s)}\\&= -0,537\, \mathrm{m/s} \approx \underline{\underline{-0,54\, \mathrm{m/s}}}\end{align*}}$$