You seemed to have gotten the equation wrong, but don't worry I'll help you
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First you simplify the equation
4=(-1)(-3)+b
(A negative times a negative is a positive)
4 = 3 + b
(Flip the equation)
b + 3 = 4
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Then you subtract 3 from each side
b+3-3=4-3
b = 1 is your answer
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y = -1x - 7 is wrong as well
To find the answer just add -4 on each side for y+4=-1(x-3)
y+4+-4=-x+3+-4
y = -x - 1 is the answer
To graph, plot points on Y-intercept of -1 and place another point at (-2,1)