Mass: 306 g
Notice that the object's density is given in grams per cubic centimeter, but that its dimensions are given in milimeters.
In order to get the units to match, you need to calculate the volume and then convert it from cubic milimeters to cubic centimeters.
You're dealing with a rectangular prism, which means that its volume will be
In your case, you have
Convert this value to cubic centimeters
Since you know that the object's density is
Rounded to three sig figs, the number of sig figs you gave for the dimensions of the rectangle, the answer will be