A solution is to be kept between 68°F and 77°F.

Since the solution is to be kept between $68^{\circ} \mathrm{F}$ and $77^{\circ} \mathrm{F}$,

$68

Putting $\mathrm{F}=\frac{9}{5} \mathrm{C}+32$, we obtain

$68<\frac{9}{5} \mathrm{C}+32<77$

$\Rightarrow 68-32<\frac{9}{5} \mathrm{C}<77-32$

$\Rightarrow 36<\frac{9}{5} \mathrm{C}<45$

$\Rightarrow 36 \times \frac{5}{9}<\mathrm{C}<45 \times \frac{5}{9}$

$\Rightarrow 20<\mathrm{C}<25$

Thus, the required range of temperature in degree Celsius is between 20°C and 25°C.