You need to put the equation into the slope-intercept form, which is
y = mx + b
In this form, m is the slope and b is the y-intercept. You can do this by subtracting 2x from both sides of the equation in your problem (2x + y = -3). That will put it into the correct form. Try it and let me know (in the comments) what you get for the slope and y-intercept. Remember that m and b can be positive or negative numbers.
