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.