You have a large supply of very rusty 2 in. sch 40 steel pipe, which you want to use for a pipeline. Because rusty metal is rougher than clean metal, you want to know its effective roughness before...

You have a large supply of very rusty 2 in. sch 40 steel pipe, which you want to use for a pipeline. Because rusty metal is rougher than clean metal, you want to know its effective roughness before laying the pipeline. To do this, you pump water at a rate of 100 gpm through a 100 ft long section of the pipe and find that the pressure drops by 15 psi over this length. What is the effective pipe roughness, in inches?