Answer
$74Kg$
Work Step by Step
We know that
$F_b=m_1g$
$\implies F_b=(1220Kg)(9.8m/s^2)=11956N$
and $m_2=\frac{F_b}{g-a}$
We plug in the known values to obtain:
$m_2=\frac{11956N}{9.8m/s^2-0.56m/s^2}$
$m_2=1293.93Kg$
Now $m=m_2-m_1$
$\implies m=1293.93Kg-1220Kg=74Kg$
