How do I find the y-intercept if the line passes through negative 2 and 3?

Answer 1

You can't. There are an infinite number of lines that pass through the point (-2, 3).
They all have different y-intercepts and different slopes.

In order to narrow it down to a single line, you have to give more information.
One more point would do it.

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Here's the minimum information needed to define a unique line:

-- you name 2 points; I find slope, intercept, and all other points.

-- you name one point and one intercept ... 'x' or 'y'; I find slope and all other points.

-- you name x-intercept and y-intercept; I find slope and all other points.

-- you name one point and the slope; I find intercept and all other points.

-- you name one intercept and the slope; I find all other points.