Level flight question

No.14047785 ViewReplyOriginalReport
So, the question is Cl of prop aircraft at h=0 and speed 100ft/s at level flight.
But what i dont understand is,
If W=L, weight will decrease with the fuel, eventually having W<L, which would pitch the aircraft. Should i assume mass with fuel, mass without fuel, an average or what? I looked lectures and books and cant find am answer.