Math Help - trig and mitre angles

Hi all,
I just have some basic trig behind me, and i would like some understanding on how to do some calculations.
I will insert an image as my basic model.



Being that the included angle is 155 degrees and the 7 inches and 4 inches are constants.
I would like to know how to claculate for:
angle A
angle B
and "L"
in 3 different calculations.
I would really appreciate some help on this and keep in mind, that I only have basic trig
Thanks

sin (A) =7/L
cos (B-90)=4/L
A+B+155=360

MaxJasper,
Thank you, you won't believe how helpful that was.
I have spent many hours (probably around 14) on a different forum trying to get that answer.
Your answer makes sense to me, others were trying to make a molehill into a mountain and they lost me by making the problem bigger than it was.

now, my solving for 2 unknowns with 3 equations is weak ( many many years since I've done it)
would you mind walking me throught the steps to solve for "L"?
thank you

Solve to obtain L = 8.9312"

How did you get the answer?
I don't want the answer, I want to learn how.
Thanks.

can some one give me the equation to solve for L and I will try and figure it out
thanks