we know that
[area of a circle]=pi*r²
for radius r=6 units
[area of a circle]=pi*6²-----> 36*pi unit²
the shaded region has a central angle of (360°-120°)-----> 240°
so
if 360° (full circle) has an area of---------------> 36*pi units²
240° (shaded region)-------------------------> X
X=240*36*pi/360--------> x=24*pi units²
the answer is
24*pi units²