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

Linear because x moves up by 3 and y moves up by 7
For this case we have the following numbers:
299
388
Let's round up each of the numbers to the nearest hundred,
We have then:
299 = 300
388 = 400
We note that now we have two numbers whose approximation is easier to add.
We have then:
300 + 400 = 700
Answer:
The sum of 299 + 388 is approximately:
700
4 people = 480 grams of pasta
1 person = 480 ÷ 4 = 120 grams of pasta
14 people = 120 x 14 = 1680 grams of pasta
1680g = 1680 ÷ 1000 = 1.68 kg
Answer: 1.68 kg of pasta