Which line is perpendicular to a line that has a slope of 3 and a y intercept at (0,0)

Hello :
 the line has a equation : y = ax (a y intercept at (0,0))
the slope is : - 1/3  ( product the slope = -1 a×3 = -1)
the equation is : y = (-1/3)x

Abit confused about what you mean, but i think you might be referring to slope intercept form: y = mx + bin that case b, or the y intercept is already given.(0,-1)find the slope by using the formulay2 - y1/x2 - x1the final slope will be 4/2, equivalent to 2.now your equation should look like thisy = 4/2x -1sorry if this didn’t you out!