1. The problem statement, all variables and given/known data Ok, so I have a=2bc^3 and b= c/f but I want to get rid of the b's. 2. Relevant equations So I know I do a=2(c/f)c^3 3. The attempt at a solution This is where I get lost (and feel stupid). Does this get simplified to (2c^4)/f? Or, is does it stay the same because the (c/f) is in brackets. I have to differentiate after, which is in itself another problem. Thanks!