To solve this equation, we first simplify both sides of the equation:

28 - 12x = 35.5 - 10.5 + 3x
28 - 12x = 25 + 3x

Next, we'll combine the x terms by adding 12x to both sides of the equation:

28 - 12x + 12x = 25 + 3x + 12x
28 = 25 + 15x

Subtract 25 from both sides of the equation:

28 - 25 = 25 - 25 + 15x
3 = 15x

Finally, divide both sides by 15 to solve for x:

3/15 = 15x/15
x = 0.2

Therefore, the solution to the equation is x = 0.2.