114cm /1.14m
If we call the length of the first shelf x, shelf two is 2x+18, shelf 3 is x-12 and shelf 4 is x+4.
The total length of board is 250cm
the total length of the shelves is 5x+10 and the whole board is used so 5x+10 = 250
5x = 240 (-10 from both sides)
x = 48 (divide both sides by 5)
board 2 is 2x+18
2 x = 96+18
= 114cm