The wall shear stress in a fully developed flow portion of a 12 -in.-diameter pipe carrying water is \(1.85 \mathrm{lb} / \mathrm{ft}^{2}\). Determine the pressure gradient, \(\partial p / \partial x\), where \(x\) is in the flow direction, if the pipe is

(a) horizontal,

(b) vertical with flow up, 

(c) vertical with flow down.