Distance to the bed? (1.20 m) with knee wall 1.00 m & roof pitch 38°

So you have the drawing?

Then accurately draw the 1.20m line parallel to the floor, see where it meets the roof slope, draw the fall line downwards and measure to the wall!
You only need a simple ruler, no set square...

The mathematical calculation for this is done using the tangent

Tangent of the angle = opposite side (height) / adjacent side (distance)
TAN 38° = 20cm / x

Rearrange the whole thing for the distance (x)

x = 20cm / TAN 38°
x = 25.6cm

Thank you, now the electrical planning can continue or is now almost finished

Wow, Musketeer, can you calculate the tangent in your head????

Ms. Dipl.-math. Climbee is deeply impressed and bows humbly!

Wow, Musketeer, can you calculate the tangent in your head????

Mrs. Dipl.-math. Climbee is deeply impressed and bows humbly!

Unfortunately not in my head. I confess, I even had to briefly check whether to use sine or tangent, but thanks to Wikipedia and the Windows calculator in scientific mode, it was quickly calculated.

OT: I used to love doing math passionately and regularly scooped prizes at math olympiads. From 11th grade onwards in the advanced course, I somehow lacked practical relevance and that’s when the fun in math faded away.