Let, it will take 'x' months to save 1,06,200 Tk.
From the savings we get a series.
Such as 1200+ 1300 +1400+...........
Where, a = 1200 Tk & d=1,300 - 1,200 = 100 Tk
We know that, summation = n2{2a(n-1)d}
According to the question,
n2{2a(n-1)d}⇒n2{2×1200+100(n-1)}=106200⇒n(1200+50n-50)=
(Time ie: n cannot be negative)
So, the required time = 36 months = 3 years ans.