1) In a proportion: y/x=k
k is your constant of proportionality.
x is your independent variable and y is your dependent variable.
Since you need 3 oz of flour for each 2 oz of sugar, y=3 and x=2.
So k=1.5 (3/2)
3)
a) y/x as a showed above. This question is very similar to #1.
b) y/x=k