It is 5
2x2 -4x +6-1= 0 is the standard form
4x^2 + x + 3 = 0
x = [-1 +/- sqrt (1^2 - 4 * 4 * 3)] / 8 = - 1 +/- sqrt ( --47) / 8
= ( - 1 +/- sqrt47i) / 8 = -0.125 + 0.857i , -0.125 - 0.857i
We can solve using proportions

or 4 works is to 10 hours as 5 workers is to x hours.
to solve we cross multiply to get

so it will take 5 men 12.5 hours!