Answer:
Answer is 3% more peat and 9% more vermiculite.
Explanation:
The weight of the initial potting mixture is not given, but the percentage amounts of peat moss & vermiculite are given.
The weight of the new potting mixture is 100lb.
For the new mixture to have 15% peat and 15% vermiculite,
The amount of peat that must be added is 3% of the peat in the initial mixture.
Hint: subtract 12 from 15. Retain the percentage sign.
The amount of vermiculite that must be added is 9% of the vermiculite in the initial mixture.
Hint: subtract 6 from 15. Retain the percentage sign, as that is the scale of measurement here.