\[(3 - 2x) + (4 - 3x) + (5 - 5x) =\]
\[= 12 + 7x\]
\[3 - 2x + 4 - 3x + 5 - 5x = 12 + 7x\]
\[- 10x - 7x = 12 - 3 - 4 - 5\]
\[- 17x = 0\]
\[x = 0.\]