The order for first section of questions is as shown below:
G
C
A
F
D
H
E
B
Following the same logic, we can solve the second part to this question:
a+b+c = 30
a+b = 30 - c
a^2 + b^2 + 2ab = 900 - 60c + c^2
a^2 + b^2 = c^2
Therefore : c^2 + 2ab = 900 - 60c + c^2
2ab = 900 - 60c
Once you divide by 2, you get : ab = 450 - 30c
Area of a right angled triangle = ab/2
Once you divide by 2, you get : 225 - 15c
Therefore, The perimeter is 30 units and the Area is 225 - 15c
Extension
Again, using the same logic, we can solve the extension:
a+b+c = p
a+b=p-c
Squaring both sides : a^2+b^2+2ab=p^2+c^2-2pc
Pythagoras theorem : a^2+b^2=c^2
Therefore, c^2+2ab=p^2-2pc +c^2
So 2ab=p^2-2pc
ab=(p^2-2pc)/2
ab=p^2/2 - pc
Area of right angled triangle : ab/2
Therefore : ab/2 = p^2/4 - pc/2
ab/2 = (p^2 - 2pc)/4
Therefore, Area of a right angled triangle is equal to : p/4 (p - 2c)