An asymptote of a function is a line to to which the function converges to as it tends to infinity such that the function gets infinitesimally close to its asymptote but the function will not reach or cross its asymptote. That is the separating distance between the function and the asymptote tends to zero as either the x or y coordinates, or both the x and y coordinates tend to infinity.
A vertical aymptote, is one parallel to the y-axis and it is given by the value of the x-coordinate where it occurs
In the graph of the question, the vertical asymptote occurs at x = 12 and it is the line x = 12.
