1st month : 5000(1+6%/12)=5000(1.005)
2nd month : [5000(1.005)+5000](1.005) = 5000(1.005)^2 + 5000(1.005)
...
24th month : 5000(1.005)[(1.005)^23+(1.005)^22+...+1] = 5000(1.005)[(1.005)^24-1]/(1.005-1)=127795.5751
2年後,佢第一天就有租金, so + 5000
= 132795.5751 ~133000

我唔太肯定

C = a r^2 + b r^3 (where a,b are real number)
96 = 16a + 64b
3 = a + b
on solving, a = 2, b = 1
=>
C = 2 r^2 + r^3
when r = 2
C = 16
when r = 6
C = 288

the volume of the spare : (4pi r^3)/3
when r = 2 , volume A = (4pi 2^3)/3 ( let A be the volume of the spare that r = 2)
when r = 6, volume = (4pi 6^3)/3=[(4pi 2^3)/3](3^3) = 27 A
=>the resource that making a r = 6 's spare can make 27 r = 2's spare
=>hving the same resources, the cost that making 27 r=2's spare = 27x16 = 432
the % increase of cost :
(432 - 288)x 100%/288 = 50%

用開英文..sorry..