Calculate the specific rotation of glucose given the observed rotation, mass, volume, and path length.

Observed rotation ($\alpha$) = $+13.6^\circ$
Mass of glucose = $8 \text{ g}$
Volume of methanol = $100 \text{ mL}$
Path length of polarimeter tube ($l$) = $2 \text{ dm}$

The concentration is given in g/mL.

The specific rotation $[\alpha]$ is calculated using the formula:

where $\alpha$ is the observed rotation, $l$ is the path length in decimeters (dm), and $c$ is the concentration in g/mL.

The specific rotation of glucose is $85^\circ \text{ dm}^{-1} (\text{g/mL})^{-1}$.

The calculated specific rotation is 85. This matches option (A).

The final answer is $\text{A}$