It's a hexagon.
The formula of the sum of internal angles in the polygon:

Therefore

I haven’t met them but they seem like very nice fun people ...
Have you met them? :)
Simplify 5/10 to 1/2
find the LCD of both fractions and that would be 18
make the denominators the same as the LCD
Simplify, now denominators are equal
join the denominators
simplify it now (23/-18)
convert to mixed fraction
Answer: -1 5/18.