A lake has a volume of10^8 m^3. A river flows into the lake at the rate of310^5 m^3/day.

. The same amount of pure water evaporates from the lake each day, so the volume of the lake does not change. The river contains 7 % pollution. The lake is initially unpolluted.

(a) What is the percentage pollution in the lake after t days?__________%

(b) When does the pollution in the lake reach 1%? after______days