Concept: The question tests on the fundamentals of Coordinate Geometry
Equation of a line = y = mx + c
Since the line is passing through the origin, c = 0 and y = mx
Also given that the line passes through the points (6, 60).
Putting it in the above equation, 6 = m*6. Therefore m = 1 and the equation of the line is y = x
Now if the function is defined as f(x) = y = x + 3, then y = x is defined by f(x - 3)