Direct Variation
If y varies directly with x, then they are related by the equation:
y = kx
Where k is a constant called the proportionality factor.
It's given that y = -38 when x = 19. Substituting those values in the equation, we can find the value of k:
-38 = k*19
Dividing by 19:
k = -38 / 19
k = -2
Now our model is complete:
y = -2x
Now it's required to find the value of x when y = -4. Substituting:
-4 = -2x
Dividing by -2:
x = -4 / (-2)
x = 2