Answer:
Let the length of the first shelf = x
Length of second shelf = 2x + 18
Length of third shelf = x - 12
Length of remaining shelf = x + 4
Since Robert has to use a board of 2.5 m , the sum of lengths of all these shelves should be 250 cm
<em>So, x + 2x + 18 + x - 12 + x + 4 = 250 </em>
<em>5x + 10 = 250</em>
<em>5x = 240</em>
<em>x = 48 cm</em>
Therefore, the length of the first shelf should be 48 cm
Kindly Mark Brainly, Thanks
