The same equation can be written in different ways.
Sometimes, for homework, you are asked (or expected) to write your answer in a specific way.
One format is called the "slope intercept"
y = mx + c
where m is the slope (how fast y increases when x goes up by 1)
and c is the intercept (the value of y, when x=0)
Yours appear to be
y = (-2/3)x + 4
From there, you can go to any of the other "standard" formats.
Multiply both sides by 3
3y = -2x + 12
Add 2x to both sides
2x + 3y = 12
(this is, apparently, the format you were expected to use)
Subtract 12 from both sides
2x + 3y - 12 = 0
(This is also known as a standard format).
If anything, you try to avoid fractions (if you can); also, if you are stuck with using a fraction, you try to make it a ratio of integers
(I suspect that your 0.666 was meant to represent 2/3, which is really 0.66666666666... forever)
In other words, 0.666 is not quite the same as 2/3.