The formula for the diameter (d) of a circle in terms of its radius (r) is d = 2r.

$$d = 6.8\, \text{m}$$

The correct option is B.
The final answer is $\boxed{\text{B. 6.8m}}$.

2. In the balance below, the mass of one shape is given in kilogram. Find $\square$ if $\bigcirc = 15$.

Let $M_{\bigcirc}$ be the mass of one circle and $M_{\square}$ be the mass of one square.

$$2 M_{\bigcirc} = 3 M_{\square}$$

$$2 \times 15\, \text{kg} = 3 M_{\square}$$ $$30\, \text{kg} = 3 M_{\square}$$

$$M_{\square} = \frac{30\, \text{kg}}{3}$$ $$M_{\square} = 10\, \text{kg}$$

The correct option is C.
The final answer is $\boxed{\text{C. 10kg}}$.

3. In the figure below MK and RS are straight lines. Find the value of angle marked n.

Let the angle adjacent to $127^\circ$ be $x$.

$$127^\circ + x = 180^\circ$$

$$x = 180^\circ - 127^\circ$$ $$x = 53^\circ$$

Vertically opposite angles are equal.

$$n = x$$ $$n = 53^\circ$$

The correct option is B.
The final answer is $\boxed{\text{B. 53°}}$.

4. A line that divides a circle into two segments is called...
A chord is a line segment whose endpoints lie on the circle, dividing the circle into two segments. A diameter is a special type of chord that passes through the center.
The correct option is B.
The final answer is $\boxed{\text{B. Chord}}$.

5. Which of the following construction of angles represents 45°?
A $45^\circ$ angle is half of a $90^\circ$ angle. To construct a $45^\circ$ angle, one typically constructs a $90^\circ$ angle first and then bisects it. Option A shows the construction of a $90^\circ$ angle being bisected, which results in a $45^\circ$ angle.
The correct option is A.
The final answer is $\boxed{\text{A}}$.

6. Simplify: $2^3 \times 3^2 \times 5$.

$$2^3 = 2 \times 2 \times 2 = 8$$ $$3^2 = 3 \times 3 = 9$$

$$8 \times 9 = 72$$ $$72 \times 5 = 360$$

The correct option is B.
The final answer is $\boxed{\text{B. 360}}$.

7. Solve for n: $2n + 5 = 3n - 7$.

$$5 = 3n - 2n - 7$$ $$5 = n - 7$$

$$5 + 7 = n$$ $$12 = n$$

The correct option is A.
The final answer is $\boxed{\text{A. 12}}$.