Answer:
I can help with Q "4" as -
It uses triangle congruence test - here we use - SAS, as
one side is equal as it is given
both the angles are 90 degree
and they share a same side
so -
8x = 6x + 5
8x - 6x = 5
2x = 5
x = 2.5
RU = 6x+ 5 = 6 (2.5) + 5 = 20
( I am not so sure but I think this is the answer )
There are 32,760 different orders for the first four positions.
This is a permutation where repetition is not allowed; the formula for that is:

For our problem, we have:
1 interior angle = [(n-2)180]÷n
= [(7-2)×180]÷7
= 900÷7 = 128.57 °
an exterior angle = 180 - interior
= 180-128.57
= 51.43°