How do I subtract the time difference from another time difference?

i.e -

I have 6:34pm (time I left) in G12 and I have 8:58am (time I came in) in
G11. I found the difference between the two times by using formula:
=TEXT(G12-G11,"h:mm"), which gave me 9:36. So this is telling me I worked 9
hours and 36 minutes for that day.

Now I want to calculate how long my lunch break was, since I do not get paid
for it, which is below:

I have 1:44pm (time I came back from lunch) in G15 and I have 1:05pm (time I
left for lunch) in G14. I found the difference between the two times by using
formula: =TEXT(G12-G11,"h:mm"), which gave me 0:39.

Now I know I was at work for 9 hours and 36 minutes, but had a 39 minute
lunch break. What formula could I use to show me exactly how many hours and
minutes I really worked?

The formula should show me that I really worked 8 hours and 57 minutes.

Any ideas??