Y = 4 - 2X 2X = 4 - Y --> X = 0.5 * ( 4 - Y) = 2 - 0.5Y ............................................................................................. X = 9 - 6Y 6Y = 9 - X --> Y = 1\6 * ( 9 - X) = 9\6 - 1\6X = 1.5 - 1\6X ....................................................... B = 12 - 3A 3A = 12 - B --> A = 1\3 * ( 12 - B ) = 4 - 1\3B .................................................................... C = 15 - 8D 8D = 15 - C --> D = 1\8 *(15 - C ) = 15\8 - 1\8C = 1.875 - 1\8C