Answer: 6
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Work Shown:
(whole length)*(external part) = (whole length)*(external part)
(EG)*(FG) = (SG)*(HG)
(2x+4)*(4) = (x+5)*(5)
8x+16 = 5x+25
8x-5x = 25-16
3x = 9
x = 9/3
x = 3
Use this x value to find EF
EF = 2x
EF = 2*3
EF = 6
For more information, search out "secant secant formula". It's not a typo that I wrote "secant" twice.