A syringe contains 2.60 mL of gas at 20.0°C. What is the volume of gas after the temperature is increased to 68.0°C?

${V}_{2} \cong 3 \cdot m L$
From old $\text{Charles' Law}$ we know that $V \propto T$, or $V = k T$ for a given amount of gas at constant pressure. If we solve for $k$, then ${V}_{1} / {T}_{1} = {V}_{2} / {T}_{2}$, and ${V}_{2} = {V}_{1} / {T}_{1} \times {T}_{2}$.
Of course, we must use $\text{absolute temperatures}$, ${T}_{1} = \left(20.0 + 273.15\right) \cdot K$, and ${T}_{2} = \left(68.0 + 273.15\right) \cdot K$. And thus.......
${V}_{2} = \frac{2.60 \cdot m L}{\left(20.0 + 273.15\right) \cdot K} \times \left(68.0 + 273.15\right) \cdot K = 3.03 \cdot m L$