A = cross sectional area of the pipe. When the pressure is expressed in terms of the equivalent height of a column of that fluid, as is common with water, the friction loss is expressed as S, the "head loss" per length of pipe, a dimensionless quantity also known as the hydraulic slope.
Find the slope first by doing (6+2)/(4-3)=8/1 or just 8. Next use a set of coordinates into the equation so 6=8(4)+b then solve so 6=32+b next subtract 32 from both sides which would equal -24=b. Then plug it all into the equation so y=8x-24
