Before leaving to visit mexico levantine traded 270 america dollars for 3000 mexican pesos when returning for mexico he had 100 pesos left how much will he receive when he exchanges theses pesos for dollars

First, you have to calculate what one American dollar is worth in pesos. 3000 pesos = 270 American dollars, so 3000pesos/270american dollars = 11.1111 so one American dollar is worth 11.1111... pesos. Calculating how much he has left in American dollars, 100pesos / 11.1111 (1 American dollar in pesos) = 9. He has 9 American dollars.
TIP: You would think it would equal 9.000000000001 but since the zeroes go on forever, the one never comes up, which makes it equal to 9.