If you already have the x and y intercepts, you can use a formula to figure the equation out

$${x\over a}+{y\over b}={1}
$$

"a" would be the x intercept and "b" would be the y intercept

$${x\over 1.5}+{y\over -3}={1}
$$

multiply 2 on the top and bottom of

$${x\over 1.5}
$$

So you get

$${2x\over 3}
$$

Then using this info we get

$${2x\over 3}+{y\over -3}=1
$$
$${2x-y\over 3}=1
$$
$${2x-y}=3
$$

After rearranging things, we get

$$y={2x-3}
$$

And that's it!