lets say that the first number is x and the second number is y.
from the question we know that:
y=-3x and x+y=-4
from there, you need to replace the y in the second equation with -3x since we know that is what y equals so we can have an equation with only one variable.
x+-3x+-4
Then you solve for x.
-2x=-4
x=2
then you find y with the fact that y=-3x
y=-6
