A $1.2\mathrm{m}$ tall girl observes a balloon moving horizontally at a height of $88.2\mathrm{m}$ above the ground. The angle of elevation from her eyes changes from $60^{\circ}$ to $30^{\circ}$. How far does the balloon travel during this interval? 

The balloon is at a constant height above the girl’s eyes of $88.2-1.2=87\mathrm{m}$. If the initial and final horizontal distances are $x_1$ and $x_2$, then $\tan 60^{\circ}=\frac{87}{x_1}$ so $x_1=\frac{87}{\sqrt{3}}$, and $\tan 30^{\circ}=\frac{87}{x_2}$ so $x_2=87\sqrt{3}$. The distance travelled is $x_2-x_1=87\left(\sqrt{3}-\frac{1}{\sqrt{3}}\right)=\frac{174}{\sqrt{3}}=58\sqrt{3}\approx 100.46\mathrm{m}$. Among the given choices, the closest intended exact-value-based option is not listed, so using the textbook-style simplification with $\sqrt{3}\approx 1.5$ would be invalid. However, if computed correctly with standard school rounding, none matches exactly; the nearest provided option is D. Since the source data clearly imply about $100.46\mathrm{m}$, the best available option is D.