Question

density = mass / volume
the density of water = 1 g/ml
because the density of water is exactly 1, the volume and mass of water will be equal to one another.
note: 1 ml = 1 cm³, so you may sometimes see density written as g/cm³ as well.
density mass volume
water 1 g/ml 20 g
water 1 g/ml 15 ml
substance a 4 g/ml 100 g
substance b 2 g/ml 5 ml
substance c 3g 1 ml

Explanation:

Step1: Recall density formula

Density $
ho=\frac{m}{V}$, where $
ho$ is density, $m$ is mass and $V$ is volume. We can re - arrange it to find mass $m =
ho\times V$ and volume $V=\frac{m}{
ho}$.

Step2: Find volume of 20 g water

For water with $
ho = 1\ g/mL$ and $m = 20\ g$, using $V=\frac{m}{
ho}$, we have $V=\frac{20\ g}{1\ g/mL}=20\ mL$.

Step3: Find mass of 15 mL water

For water with $
ho = 1\ g/mL$ and $V = 15\ mL$, using $m=
ho\times V$, we get $m = 1\ g/mL\times15\ mL = 15\ g$.

Step4: Find volume of 100 g of Substance A

For Substance A with $
ho = 4\ g/mL$ and $m = 100\ g$, using $V=\frac{m}{
ho}$, we obtain $V=\frac{100\ g}{4\ g/mL}=25\ mL$.

Step5: Find mass of 5 mL of Substance B

For Substance B with $
ho = 2\ g/mL$ and $V = 5\ mL$, using $m=
ho\times V$, we have $m = 2\ g/mL\times5\ mL=10\ g$.

Step6: Find density of Substance C

For Substance C with $m = 3\ g$ and $V = 1\ mL$, using $
ho=\frac{m}{V}$, we get $
ho=\frac{3\ g}{1\ mL}=3\ g/mL$.

Answer:

Density	Mass	Volume
1 g/mL	15 g	15 mL
4 g/mL	100 g	25 mL
2 g/mL	10 g	5 mL
3 g/mL	3 g	1 mL