Given that,

Power of GSL bulb, $P_1 = 60\ \text{W} = 0.06\ \text{kW}$

Power of CFL bulb, $P_2 = 13\ \text{W} = 0.013\ \text{kW}$

Cost of GSL bulb = Tk. 30

Cost of CFL bulb = Tk. 250

Cost of electricity per unit = Tk. 4

The additional cost for buying the CFL bulb is,

$$ \begin{aligned} \text{Additional cost} &= 250 - 30 = 220\ \text{Tk} \end{aligned} $$

The power saved by replacing the GSL bulb with the CFL bulb is,

$$ \begin{aligned} \Delta P &= 60\ \text{W} - 13\ \text{W} = 47\ \text{W} = 0.047\ \text{kW} \end{aligned} $$

Let the bulb be used for $h$ hours daily. The energy saved in one year (365 days) is,

$$ \begin{aligned} \text{Energy saved} &= \Delta P \times h \times 365 \\ &= 0.047 \times h \times 365\ \text{kWh} \end{aligned} $$

The money saved from electricity in one year must equal the additional cost of the bulb:

$$ \begin{aligned} \text{Money saved} &= \text{Energy saved} \times 4 \\ 220 &= (0.047 \times h \times 365) \times 4 \\ 220 &= 68.62 \times h \\ h &= \frac{220}{68.62} \\ h &\approx 3.206\ \text{hours} \end{aligned} $$

Thus, the CFL bulb must be used for approximately $3.206$ hours daily to recover the cost within one year.