A: no solution!
first, simplify each side of the equation.
3x + 5 - 10x simplifies to -7x + 5.
8 - 7x - 12 simplifies to -7x - 4.
then, add +7x on both sides of the equation to get the variable alone. if you add 7x to each side, you get left with 0.
so, that leaves 5 = -4 which is not true. so, that means there is no solution.