3f + 2g = 30 . . .(1)
f + 2g = 26 . . . .(2)
(1) - (2) => 2f = 4 => f = 4/2 = 2
From (2), 2 + 2g = 26 => 2g = 26 - 2 = 24 => g = 24/2 = 12
Therefore, f = 2 and g = 12
We can split this up into 3 rectangles. 2 vertical ones (8 x 3) and one horizontal one in the middle (5 x (8 - 5)
8 x 3 = 24
24 x 2 = 48
5 x (8-5) = 5 x 3 = 15
now add 48 + 15 = 63 cm^2
A15=243
74-61=13
87-61=13
So they're adding 13 every time.
A15 is 11 terms from A4 which is the last one you are given so 11*13=143
143+100=243
