Маша прочитала первый том за 20 дней. Чтение второго тома заняло у неё 15 дней. Все три тома она прочитала за 45 дней. За сколько дней прочитала Маша третий том?

Russia is very big country.It has a lot of cities and towns.Also,it has many different beautiful places.For example,Mamaev Hill,Eernal Flame and Panorama in Volgograd,Kremlin and Mausoleum in Moscow,Hermitage and Petergof in S-P.I think that Hermitage is very beautiful and exciting build in the world!There are many brilliant  sights,things and paintings.I like Saint-Pererburge!