Slope of point P is 4/11.
Points do not have slopes.
Is it slope of altitude?
One should know the value of m and b.you have calculated m=4/11.but still don't know b.
By 7=4/11(3)+b we can get value of b that is
now put the value of m and b in y=mx+b and you will get the desired equation.now any problem?Feel free to ask.