The Jacobian for this transformation is

with determinant
, hence the area element becomes

Then the integral becomes

where
is the unit circle,

so that

Now you could evaluate the integral as-is, but it's really much easier to do if we convert to polar coordinates.

Then

The last option because he spent $135 or more
Answer:
5 apples
Step-by-step explanation:
4 friends + Robby = 5 people
25 apples in total ÷ 5 people
= 5 apples per person