3 : 8....can be written as 3/8
12 lbs of apples were sold
apples / oranges : 3/8 = 12/x
this is a proportion, so we cross multiply
(3)(x) = (12)(8)
3x = 96
x = 96/3
x = 32 <=== 32 lbs of oranges
notice that 3/8 = 12/32....these are equivalent fractions....because that is what proportions are, equivalent fractions