First, we combine like terms:

12х - 5.9 - 7.5х + 3.2 = -4.05

Next, we simplify the equation:

4.5х - 2.7 = -4.05

Now, we isolate the variable by adding 2.7 to both sides:

4.5х = -1.35

Finally, we solve for x by dividing by 4.5:

x = -1.35 / 4.5
x = -0.3

Therefore, the solution to the equation is x = -0.3.