antiflux

If in a subtilisin enzyme assay at pH=8.6 and 25C (both optimal), the absorbance of the solution increased by 0.43 @ 410nm in 1 min, what was the rate of the reaction expressed as Δ[product]/min? The diameter of the assay tube placed in the spectrophotometer was 1cm. I'm confused because the question doesn't give any concentrations, so how can i calculate the rate??