Since the death rate is higher than the birth rate we can assume that it will be negative. 5-15 is -10 for their life. immigration is also lower than the emigration. 2-4 is -2. adding -2 and -10 will give us -12, hope this helps.
To make ATP, cells must join together ADP & a phosphate using energy from food. A phosphate is removed from an ATP molecule in order to provide energy for the cell. Thus, the ATP molecule turns into an ADP molecule. We eat food which gives us energy to add another phosphate group to the ADP molecule, turning it into an ATP molecule. The cycle then begins again.