12. One brand of horse feed is made of oats and barley. The ratio of oats to barley is
4:11 by mass. How many kilograms of each grain are needed to make 150 kg of
feed?

The percent increase is actually 9.701.  Here's the formula for it:
% Increase = [(New number - original number)/(original number)] all multiplied by 100.  Our situation looks like this: %Inc = (308.7-281.4)/281.4 which gives us %Inc = 27.3/281.4  That comes out to %Inc = .0970149; now multiply it by 100 to change it to a percent to get a percent increase of 9.701%