Since there is 1 whole pan of spinach pie, you would subtract 3/5 from 1 to find out how much was left after the party:
1-(3/5)=2/5
That is how much spinach Rose has left from the party.
Now, she has 2/5 of the spinach pie left, and her family gets 3/4 of what is left, so you need to find out how much 3/4 of 2/5 is:
(2/5)*(3/4)=6/20=3/10
Using this number, subtract is from 2/5 and you get how much is going to be used to made the salad:
(2/5)-(3/10)=(6/10)-(3/10)=3/10
Rose used 3/10 of the Spinach pie to make the salad.