perpendicular lines have slopes that multiply to -1
get into y=mx+b form
minus 15x both sides and divide by -5
y=3x-7/5
slope is 3
3 times what=-1?
what=-1/3
so the slope is -1/3
so
y=-1/3x+b
we use the point (0,-4)
x=0 and y=-4
-4=-1/3(0)+b
-4=b
y=(-1/3)x-4 is da equation
