A soil scientist mixes three compost types to achieve a target C:N ratio of 25:1. Compost A has a C:N of 30:1, Compost B is 20:1, and Compost C is 15:1. She uses 40 kg of A, 35 kg of B, and 25 kg of C. What is the weighted average C:N ratio of the final mixture? - Groen Casting