$\begin{cases}H_2NC_3H_5(COOH)_2:x mol \\H_2NCH_2COOH:(0,3-x) mol \end{cases}\Rightarrow \begin{cases}n_{-NH_2}=0,3 mol \\n_{-COOH}=(0,3+x) mol \end{cases}$$*)0,3>x\geqslant 0,1\Rightarrow m=m_X+m_{HCl}+m_{NaOH}-18.0,8$
$*)0<x<0,1\Rightarrow m=m_X+m_{HCl}+m_{NaOH}-18[0,8-(0,8-0,4-0,3-x)]$
$\Rightarrow m=m_X+m_{HCl}+m_{NaOH}-18(0,7+x)$