0.8x0.4xC + 0.6G =35 (C for full chicken feed and G for goat feed)
there are two significant problems with this approach.
first of all, you shouldn't have 0.6g; you should have 0.6 times all
the money that the farmer spent.
right now, you are taking 60% of the money that the farmer spent on goat feed
, which doesn't represent anything in the problem. (as an analogy, if an item is on sale for 75% of regular price at a store, then 75% of the sale
price would be a meaningless quantity -- since it's the sale price that is 75% of some other quantity.)
second -- even if you make that substitution, this approach still won't work, because your two terms are inconsistent with each other.
in the first term, you are attempting to work with a variable that represents the entire full-price
cost of the feed (as opposed to what the farmer actually paid). in the second term, however, the goat feed is not 60% of the theoretical full-price cost; it's 60% of how much the farmer actually paid.
so, in other words, your first term uses the amount that the farmer would
have paid, while your second term uses the amount that the farmer actually did
pay. that's not workable.