Answer:
(181,264,245) or x=181 y=264 z=245
Step-by-step explanation:
a) Clearly define your variables.
x=section a
y=section b
z=section c Â
b) Write a system of equations.
x+y+z=690
20x+15y+10z=10,030
x+328=y+z ---> x-y-z=-328
c) We can solve using a matrix.
The numbers in parenthesis are what go in the matrix.
x(1)+y(1)+z(1)=690(690)
20x(20)+15x(15)+10x(10)=10,030(10,030)
x(1)-y(-1)-z(-1)=-328(-328)
(Pretend that the lines are not broken and look like this [])
    (⎡ 1  1  1    690   ⎤) Â
rref (⎢20 15 10  10,030 ⎥)
   (⎣ 1  -1  -1   -328   ⎦)
Answer(Matrix): ⎡1 0 0  181 ⎤
             ⎢0 1 0  264⎥
             ⎣0 0 1  245⎦
Or you could solve without using a matrix: