Interest Rate Swaps

I wondered if you could please help with this question & answer.
Question
James has £5m investment that pays Libor + 4%
Joe has a £6m investment that pays fixed rate of 6% per month
James & Joe agree to enter an interest rate swap
What is Libor if James pays Joe £40,000.

Answer
Work out the fixed interest of 6% = £6m x 6% = £360,000
So Joe gains interest of £360,000. We also know that James pays £40,000 to Joe as they’ve promised to swap interest.
That means that the interest James earns must be £400,000(£360,000 +£40,000)
Now that we know this we can work out the Libor rate
£5m x (Libor + 4%) = £400,000. So £400,000/£5,000,000 = 0.08 = 8%
Libor + 4% = 8%. So Libor = 4%

I do not understand how they arrived at the fact that James must have paid £400,000
Can you help me?
Thanks