App.of integration

1) The volume of water in lake is 2.2x10^10 m^3 on 1 January2009. The
rainfall to the lake is modelled to be [1.3x10^7-1000(t-180)^2] m^3 per day,water is evaporated from the lake at a rate of 1.1x10^6xe^(-t/20 000)
m^3 per day where t is the time in days.
Assume there are 365 days in a year.
a)find the rate of change of volume of water in the lake for a certain value of t.
bi)find the volume of rainfall from 1 January2009 to 31December 2009.
bii)find the volume of water evaporated from 1 January2009 to 31December 2009.
bii) find the volume of water in lake on 31 December2009.
ans: bi) 6.9x10^8
bii) 3.98x10^8
biii)2.23x10^10
pls show clear steps.thx