I don't know really ask someone smarter than me
The mileage is the independent variable. You can control it. The gasoline remaining DEPENDS ON the number of miles different. That's why it's called the dependent variable. It's change depends on the change in the independent variable
Answer:
whole number and a fraction
Make a change of coordinates:


The Jacobian for this transformation is

and has a determinant of

Note that we need to use the Jacobian in the other direction; that is, we've computed

but we need the Jacobian determinant for the reverse transformation (from

to

. To do this, notice that

we need to take the reciprocal of the Jacobian above.
The integral then changes to
