Let x be the amount of the first brand of peat and y the amount of the second brand of peat.
In the brand 1 there is x/10 of peat and in brand 2 3y/10 or 0.1x and 0.3y
In the mixture there is 2/4=1/2cu ft of peat, so 0.1x+0.3y=0.5. The amounts of the brands must come to 2cu ft so x+y=2.
That means y=2-x, which we can substitute into the other equation:
0.1x+0.3(2-x)=0.5, 0.1x+0.6-0.3x=0.5, 0.1=0.2x so x=0.1/0.2=0.5cu ft.
So y=2-x=1.5cu ft.
Let’s check if that’s right: amount of brand1 peat=0.5/10=0.05cu ft.
Amount of brand 2 peat=0.3*1.5=0.45cu ft.
Total amount of peat in the mixture is 0.45+0.05=0.5cu ft. And 0.5cu ft in 2cu ft of mixture is 1/4 or 25%.