Answer:
D
Step-by-step explanation:
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

Answer:
let t = no of minutes when they are at the same altitude
:
52200 - 3300t = 2500t
52200 = 3300t + 2500t
52200 = 5800t
t = 52200/5800
t = 9 minutes they will be at the same altitude
:
The altitude:
9*2500 = 22500 ft
:
Check on other train
52200 - 9(3300) =
52200 - 29700 = 22500 ft
1 subscription = $21
28 subscriptions = x
You know 1 subscription is $21
You want to find out how much 28 subscriptions are
Multiply 28 (subscriptions) by 21 ($ per subscription)
28 x 21 = 588
28 subscriptions cost $588
If you would like the formula to find out how many subscriptions cost hat amount of money,
21x = y
x is how many subscriptions you want, while y is the total cost of the money