modify variables

# The current volume of a water reservoir (in cubic metres)
reservoir_volume = 4.445e8
# The amount of rainfall from a storm (in cubic metres)
rainfall = 5e6

# decrease the rainfall variable by 10% to account for runoff
rainfall *= 0.9
# add the rainfall variable to the reservoir_volume variable
reservoir_volume += rainfall
# increase reservoir_volume by 5% to account for stormwater that flows
# into the reservoir in the days following the storm
reservoir_volume += reservoir_volume*0.05
# decrease reservoir_volume by 5% to account for evaporation
reservoir_volume -= reservoir_volume*0.05
# subtract 2.5e5 cubic metres from reservoir_volume to account for water
# that's piped to arid regions.
reservoir_volume -= 2.5e5
# print the new value of the reservoir_volume variable
print(reservoir_volume)