The volumes of the two geometries are the same, that is, V (cuboid) =V (cylinder).

V (cuboid) = 2.1*1.2 * 6 =15.12cm?

∴V (cylinder) =3. 14*5*r=V (cuboid) = 15. 12cm?

The solution is r=0.963= 1.0 (accurate to 0. 1CM).