??????????? yu want a strate line thru point= (5,5) ????????
& make it 90 deg from line defined as x-3y=7 ??????
or y=(x/3)-7...this slope=1/3
line 90 deg from that hav slope=-3
y=-3x+konst
projekt line from x=5 tu x=1...deltax=-5
deltay=slope*deltax=-3*-5=+15
y at this point=5+15=20
point=(0,20)
y=-3x+20