Could someone help me answer a tricky question in an online numerical reasoning test?

In this test - https://practicereasoningtests.com/p...numerical-test - question 2, I'm surprised by the answer: IT and the explanation:

IT total Supervisor base and bonus = £52940 plus £4500 = £57440 with IT Support Staff £16000 plus £800 = £16800. Differential between £57440 and £16800 is £40,640 which highlights the largest difference across all functions. Therefore, "IT" is correct.

I would expect the answer to be: Finance.

Can anyone give me a clearer explanation?

Ed.