B1. Žiga will prepare identical shelves from a board that is $30 \mathrm{~cm}$ wide and $30 \mathrm{~mm}$ thick. He will attach them to a wall in the shape of a rectangle that is $2.5 \mathrm{~m}$ high and $3 \mathrm{~m}$ wide, one above the other, with a vertical distance of $4 \mathrm{dm}$ between them. Each shelf will be $8 \mathrm{dm}$ from the right and left edges of the wall. The highest shelf will be $1 \mathrm{~m}$ from the ceiling, and the lowest will be at least half a meter but no more than one meter from the floor.

A. How many shelves will he attach to the wall in this way?

B. What is the minimum length of the board he will use to prepare these shelves?

C. What is the minimum amount of wood he will use for these shelves? Express the volume in cubic decimeters to one decimal place.

D. Žiga will stretch a non-elastic string from the upper left corner of the front part of the highest shelf to the lower right corner of the front part of the lowest shelf. How long will the stretched string be? Write the length of the string to the nearest millimeter.
B1. The bottom surface of the highest shelf will be at a height of $1.47 \mathrm{~m}$, the bottom surface of the second shelf will be at a height of $1.04 \mathrm{~m}$, and the bottom surface of the third shelf will be at a height of $0.61 \mathrm{~m}$. Each shelf will be $1.4 \mathrm{~m}$ long, and for all three together, Žiga will use at least $4.2 \mathrm{~m}$ of wood. The volume of all three shelves can be calculated using the formula $V=3 a b c=3 \cdot 1.4 \cdot 0.03 \cdot 0.3=0.0378 \mathrm{~m}^{3}$. The vertical distance between the top surface of the highest shelf and the bottom surface of the lowest shelf is $0.89 \mathrm{~m}$. The distance between the upper left corner of the highest shelf and the lower right corner of the lowest shelf can be calculated using the Pythagorean theorem $l=\sqrt{(0.89)^{2}+(1.4)^{2}} \approx 1.659 \mathrm{~m}$.

A. Žiga will attach the three shelves in the described manner. .............................................. 1

B. For preparing these shelves, he will use at least $4.2 \mathrm{~m}$ of wood. ............. $2 \mathbf{t}$

C. For these shelves, he will use at least $0.0378 \mathrm{~m}^{3}$ of wood. ................................. $1 \mathbf{t}$

D. The vertical distance between the corners is 0.89 m. ...................................... $\mathbf{t}$

The length of the wire is 1.659 m. ........................................................ 2 t

(Note: If the length of the wire is not written to the nearest mm, 1 t is deducted.)