To find the solution of the equation \( f(x) = g(x) \), we need to identify the x-coordinate of the point where the two functions intersect.
Given that the intersection point is \( (21, 4.5) \), this means that at \( x = 21 \), \( f(21) = g(21) = 4.5 \).
Therefore, the solution of the equation \( f(x) = g(x) \) is:
\[ x = 21 \]