11.11.yrs.

Let, Here,
Interest, I = 2x
Investment, P = 5x

R = 3.6 %

T =?
Total amount = 2x + 5x = 7x
According to the question,
73x = 45000
=> x $\frac{45000}{7}$
=> x = 6428.57

Investment, P = 5x = 5 X 6428.57 = 32142.85 Tk
Interest, I = 2x = 2 X 6428.57 = 12857.14Tk
Time, T = $\frac{100\times 1}{PR}$
= $\frac{100\times 12851.14}{32142.85\times 3.6}$

= 11.11 yrs