Equations b and d have the same solutions, because if you multiply both sides of b by 2 and invert the constants you'll have equation d:
b: x - 3 = 5x + 4
b*2: 2x - 6 = 10x + 8
Move -6 and +8 to the other side: 2x -8 = 10x +6 <-- this is equation d
Similarly, starting from equation a, you can obtain equation e by multiplying both sides by 2 and equation f by dividing both sides by 10.
Equation c has nothing in common with the others.
