{country albums}:{jazz albums}=2:3
3{country albums} = 2{jazz albums}
{country albums} + {jazz albums} = 45
{jazz albums} = 45 - {country albums}
3{country albums} = 2(45 - {country albums})
3{country albums} = 90 - 2{country albums}
5{country albums} = 90
{country albums} = 18