Question

Hey I'm having truble with this word problem; The number of domestic car sales from 1981-1999 in millions is modeled by the expression y=-0.1n^2 +0.11n+6.51 where n is the number of years since 1981. The number of import car sales from 1981-1999 in millions is modeled by the expression y=0.2n^2 + 2.57. Find an expression that modeles number of car sales n years since 1981. An explanation would be nice!