Answer: height = 17.5cm
Step-by-step explanation: Peter mixes blue and yellow paint in the ratio 2:3, which means:


x = 12.6L
The container is full with the two paints, so total volume:
V = 12.6 + 8.4
V = 21L
Knowing that 1L = 1dm³ and sides of cuboid is measure in cm:
V = 21dm³ = 21000cm³
Volume of a cuboid is calculated as:
V = width*length*height
Height of the container is
height = 
height = 
height = 17.5cm
The height of the container is 17.5cm.
You can plug -x - 1 for y in the first equation
2x - (-x - 1) = 10
2x + x + 1 = 10
Combine
3x = 9
Divide
x = 3
Plug 3 for x in any equation ( I'll use th second equation )
y = - (3) - 1
y = - 3 - 1 = -4
x = 3 ; y = -4
(3, -4)
I can’t the picture can you post a other one