A =
1600(21/20)³ = 2522

100 ---- 300 --- 3

             900 --- 3

                        ----

                          6 years

SI = 20 + 20

CI = 20 + 21

20
---- 1

100
---- ? => 5%

SI = 40 + 40

CI =
40 + 40 + 1.6 = 81.6

100 ---- 200 ---- 4

              400 ---- 4

               800 ---- 4

                          ------

                            12 years

Let the rate be r % p.a, 
Then
S. I = Rs (5000 — r/100 — 2) = Rs (100r) 
 C. I = Rs[5000 — (1 + r/100) ² - 5000] 
= Rs {5000 — [(1 + r/100) ² “ 1]} 
= Rs [5000 — (r²/2 + r/50)]

= Rs (r² /2 + 100r) 
(C.I) “ (S.I) = (r²/2 + 100r) “ (100r) = r²/2 
Therefore, r²/2 = 72
 => r² = 144 
=> r = 12 
Hence, Rate = 12 % p.a