A renovation company wishes to obtain sand, stone and brick for construction work. The company sends its requirements for sand, stone and brick, measured in units, to three different suppliers, AngGui, BaBao and CaiTao. Their quotations are as follows:

1. Define variables and formulate a system of linear equations representing the total price from each supplier.

Let $x$, $y$, and $z$ be the number of units of sand, stone, and brick respectively.

Based on the table, we formulate the following system of linear equations:

2. Solve the system of linear equations using a graphing calculator.

Using a graphing calculator to solve the system of linear equations, we get:
$x = 7$
$y = 8$
$z = 2$

3. State the final conclusion in the context of the problem.

The company requires $7$ units of sand, $8$ units of stone, and $2$ units of brick.

1. Determine the required units of sand, stone, and brick by solving the system of equations from part (i).

Let the units of sand, stone, and brick required be $x$, $y$, and $z$ respectively. From the given table, we formulate the system of linear equations:
$15x + 10.5y + 8.1z = 205.2$
$11x + 17.3y + 7z = 229.4$
$12x + 13y + 10z = 208$

Solving this system using a graphing calculator gives:
$x = 7$, $y = 8$, $z = 2$.

2. Identify the lowest price per unit for each material.

Comparing the prices from the three suppliers for each material:

• Lowest price for sand = $\char36{}11.00$ (from BaBao)
• Lowest price for stone = $\char36{}10.50$ (from AngGui)
• Lowest price for brick = $\char36{}7.00$ (from BaBao)

3. Calculate the total amount charged by DaoBi considering the 10% discount.

DaoBi charges $10\%$ less than the lowest price per unit for each material. Thus, the total amount to be paid is:
$\text{Total amount} = 0.9 \times [11(7) + 10.5(8) + 7(2)]$
$= 0.9 \times (77 + 84 + 14)$
$= 0.9 \times 175$
$= 157.5$

Leaving the answer to the nearest cent, the total amount is $\char36{}157.50$.