The answer is 0.25 g/cm3
The equation for finding density is mass divided by volume.
Therefore,
12 grams/ 49 cm3= 0.24489795918367 gram/cubic centimeter
you would then round this to the nearest significant figure which is the number of significant numbers you have and the highest amount of sig figs present in this equation is two sig figs. That means that you would round your answer, becasue it has a zero before the decimal which doesn't count as a significant figure, to the nearest hundredth which would be 0.25 and then you add your value after it which is g/cm3