1. The problem statement, all variables and given/known data See attached image 2. Relevant equations Δphi = 2pi(Δx/λ) + Δphi0 = 2pi(m) -- at the maximum Δphi = (m + .5) (2pi) -- at the minimum 3. The attempt at a solution The first step should be to solve for lambda, the wavelength. So I plug in the knowns: At 30 cm the amplitude is a maximum, so: Δphi = 2pi(Δx/λ) + Δphi0 = 2pi(m) Δphi = 2pi(30/λ) + Δphi0 = 2pi(m) I am not sure what to do next. I tried too many times, so it now displays the answer as λ = 80 cm, but I'm not sure why that is true. I need help on the rest. I'm just not sure what to do since I am missing more than one variable.