Adsorption on activated carbon is to be used for reducing phenol concentration in waste water from 0.04 mol/L to 0.008 mol/L. The adsorption isotherm at the operating temperature can be expressed as q = 0.025 C13; where q is the phenol concentration in solid (mol/g solid) and C is the phenol concentra- tion in water (mol/L). The minimum amount of solid (in grams) required per liter of waste water (upto one decimal place) is