Lines a and b are perpendicular. The equation of line a is y=1/3x+3. What is the equation of line b

perpendicular lines have slopes that are negative reciprocals to each other, that is, if one slope is a/b, the other is -b/a
in this case, the given slope is 1/3, so the other line's slope is -3/1, which is -3
from the graph we see that the y intercept of line b is -4, so the equation of line b is: y=-3x-4