Hi there! I'd love to help you out!
Direct variation equations can be written as:
y = kx where "k" is a constant.
We usually have to solve for "k" first. It tell as that when y = 30 then x = 10. So we will plug these into the direct variation equation and solve for k:
30 = 10k
3 = k
So now we know "k" is 3. Our direct variation equation specific to this problem now looks like:
y = 3x
Now we can solve the final part. We will plug 84 in for y and solve for x:
84 = 3x
28 = x
We now know that when y = 84, x = 28. I hope this explanation was thorough and answered all of your questions. I specialize in assisting homeschool students and am a homeschool mom myself so feel free to reach out any time you have any questions! Learn on :)