How is the length of the surface calculated in case of countercurrent

1.	How is the length of the surface calculated in case of countercurrent settling?
A.	tL<sub>p</sub>=wV<sub> </sub>/ v cos
B.	tL<sub>p</sub>=(V<sub> </sub> V sin )/ v cos
C.	tL<sub>p</sub>=w(V<sub> </sub> V sin )
D.	tL<sub>p</sub>=w(V<sub> </sub> V sin )/ v cos
Answer» E.

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