Calculate the Length of a Valley

I am trying to calculate the length of a piece of metal flashing for a valley on a building. There are two different roof pitches that create this valley. it has a 3.5/12 pitch on one side and a 4.92/12 on the other. I am not sure what pitch these two create. What I would like to do is have a formula where I could put the two pitches in it and it would give me the pitch of the other. Then I would like to calculate the length of the flashing going up that pitch. Below are the calculations that give me the degree the flashing has to be broken if it is of any help.

Valley & Hip Plate at Corners NOT Square in Plan

Pitch 1 (on 12) = 3.5
Angle 1 (°) = 16.26 S
Pitch 2 (on 12) = 4.92
Angle 2 (°) = 22.29 SS
D' (°) = 35.43
D (°) = 54.57
90 = 90
X:12
RI = 13.37 = 13.37 2.85

C6 (°) = 80.66
C6' (°) = 71.99
C8 (°) = 152.7 Results

Valley & Hip Plate at Corners NOT Square in Plan

Pitch 1 (on 12) = 3.5
Angle 1 (°) = =DEGREES(ATAN(F10/12)) S
Pitch 2 (on 12) = 4.92
Angle 2 (°) = =DEGREES(ATAN(F12/12)) SS
D' (°) = =DEGREES(ATAN(F10/F12))
D (°) = =DEGREES(ATAN(F12/F10))
=SUM(F14:F15) = 90
X:12
RI = =DEGREES((ATAN(TAN(RADIANS(F13))*SIN(RADIANS(F14))))) = =DEGREES((ATAN(TAN(RADIANS(F11))*SIN(RADIANS(F15))))) =TAN((H18*PI())/180)*12

C6 (°) = =DEGREES(ATAN(TAN(RADIANS(F15))*(1/(SIN(RADIANS(F18))))))
C6' (°) = =DEGREES(ATAN(TAN(RADIANS(F14))*(1/(SIN(RADIANS(F18))))))
C8 (°) = =SUM(F20:F21) Results

See if this works. I don't have my CADprogram on this computer or else I'd draw it up in 3D to verify.

Thank you, it worked the first time. Great Job

As I noted in my reply to your PM, my calculation is accurate (to degree that Excel can be).

Also as noted, Run_1 is the run associated with Pitch_1. If you want the run distance of the valley or hip, multiply Run_1 by V/H_run ratio. If you want to check the V/H_length per foot of v/h run, enter "=1/B4" in cell B5 for the Run_1 distance.