Idiot requires help... (petrol in diesel tank)

Registered because I have a (relatively simple) maths problem and I can't work out how to calculate it.....

I basically put a load of unleaded in my car without thinking.... (it's a diesel car) and I'm trying to work out the percentage of petrol left in the tank after adding 3 top ups of diesel.

I've tried to calculate it in Excel but I've become confused (not hard for me).

Can anyone give me an answer and a simple formula for this problem? The details are below:

My tank was literally empty.

I put in 16.74 litres of petrol (before realising).

I then topped the tank up to full with 35.53 litres of diesel.

The car seemed sort of alright.... I then drove and kept topping up the tank to full with more diesel.

I put in a further

- 6.56 litres

- 8.30 litres

- 7.04 litres

What percentage of petrol is still left in my tank?

If anyone can answer this I'd be most grateful.

Thanks in advance