So with you knowing the x-intercept which is (-1,0) that the point and the slope are -2 you're able to use and point-slope form is y-y1=slope(x-x1). Substituting all the information you have you're to get the point-slope form as y-0=-2(x-(-1)) which can be simplified to y=-2x-1 (if you need the slope-intercept form as well)
