Answer:
"$/km"
Step-by-step explanation:
He wants to model "maintenance cost" with respect to "distance"
Normally,
maintenance cost would be in currency --- dollars, pounds etc.
distance would be in kilometers, miles, meters etc.
We need to find the ratio that has the COST on top and DISTANCE on bottom
Looking at the choices,
We can eliminate 1st and 3rd immediately as it doesn't have COST on top.
That leaves us with
$/km
and
km/$
$ is in fact currency and unit for cost and km is in fact unit for distance. We need the ratio that has $ on top and km on bottom, that's the 2nd option.
So, $/km is the appropriate unit.
