Step 1 :We are given two points on the line: (1, 266000) and (11, 1370000).
Step 2 :We can use these points to find the slope of the line, which is given by the formula: \(m = \frac{y_2 - y_1}{x_2 - x_1}\), where (x1, y1) and (x2, y2) are the coordinates of the two points.
Step 3 :Substituting the given points into the formula, we find that the slope of the line is 110400.
Step 4 :Once we have the slope, we can use the point-slope form of a line to find the equation of the line: \(y - y_1 = m(x - x_1)\).
Step 5 :We can then substitute one of the points and the slope into this equation to find the equation of the line.
Step 6 :Doing this, we find that the y-intercept is 155600.
Step 7 :This means that the linear function that fits the data is: \(S(x) = 110400x + 155600\).
Step 8 :This function represents the average salary $S$ in the year $x$, where $x$ is the number of years since 1990.
Step 9 :\(\boxed{S(x) = 110400x + 155600}\) is the final answer.