point-slope form is;
y = mx + b m is the slope, b is the y-intercept
given; m = -2
y = -2x + b
the x-intercept occurs where y = 0, and you are given the point (-1, 0)
so plug this point in the equation;
y = -2x + b
0 = -2(-1) + b
0 = 2 + b
b = -2
the equation is;
y = -2x - 2
hope that helps, God bless!