$\begin{array}{1 1}M_2=\large\frac{m_2}{(m_1/M_1)}\\M_2=\large\frac{m_2}{(m_1/M_1)(-\Delta p_1/p_1^*)}\\M_2=\large\frac{m_2}{(M_1/m_1)(-\Delta p_1/p_1^*)}\\M_2=\big(\large\frac{m_2M_1}{m_1}\big)\normalsize (-\Delta p_1/p_1^*)\end{array} $