A man is five times as old as his son. If the son's age is y, set up the quadratic equation that represents the product of their ages in four years being 340.

The final answer is $\boxed{\text{D. } 5y^2 + 24y - 324 = 0}$.

Find a common denominator, which is $ab$.

Find a common denominator, which is $ab$.

To divide by a fraction, multiply by its reciprocal.

The final answer is $\boxed{\text{D. } \frac{a^2 - b^2}{b^2 - ac}}$.

Since $\triangle XYZ$ is equilateral, all sides are equal ($XY = YZ = ZX = 6 \text{ cm}$) and all interior angles are $60^\circ$ ($\angle X = \angle Y = \angle Z = 60^\circ$).

$T$ is the midpoint of $XY$, so $XT = \frac{1}{2} XY = \frac{1}{2}(6 \text{ cm}) = 3 \text{ cm}$.

In an equilateral triangle, the line segment from a vertex to the midpoint of the opposite side (a median) is also an altitude and an angle bisector.
Therefore, $ZT \perp XY$, which means $\triangle XZT$ is a right-angled triangle with the right angle at $T$.
Also, $ZT$ bisects $\angle XZY$, so $\angle XZT = \frac{1}{2} \angle XZY = \frac{1}{2}(60^\circ) = 30^\circ$.

We need to find $\tan(30^\circ)$.

The final answer is $\boxed{\text{A. } \frac{1}{\sqrt{3}}}$.

The horizontal distance (adjacent side) is $10 \text{ m}$.
The vertical height difference (opposite side) is the height of the tree minus the height of the fence.

Using a calculator:

Rounding to two decimal places, $\theta \approx 53.68^\circ$.
Comparing with the options, $53.67^\circ$ is the closest.

The final answer is $\boxed{\text{B. } 53.67^\circ}$.