Start by getting the equation x-4y=9 into y=mx+b form by isolating the y.
*Subtract x from both sides*
-4y=-x+9
*Divide both sides by -4*
y=1/4x-9/4
Do the same thing with the other equation dx-12y=14.
*Subtract dx from both sides*
-12y=-dx+14
*Divide both sides by -12*
y=d/12x-7/6
Graphs are perpendicular when their slopes are negative reciprocals. The negative reciprocal of 1/4 is -4. Therefore, d/12 must equal -4:
d/12=-4
*Multiply both sides by 12*
d=-48
Hope this helps!!
