4+5+6=15 so the amounts invested are 4/15*1200=$320 (x), 5/15*1200=$400 (y) and $480 (z).
Amount invested in z is $480.
x+y+z=700, so z+140+z=700, 2z=560, z=$280, cash inflow for z.
x+y+280=700, x+y=$420 or x+y=280+140=$420, combined inflow for x and y.
Amount invested in y is $400.