f(3)=2 and f^-1(3)=2.25
Reasoning: the line has a y coordinate of 2 for the x coordinate of 3. That gives us f(3)=2.
The inverse function requires us to find the x coordinate when the y coordinate is 3. This gives us a value a bit bigger than 2. But we can find the equation of the graph. The slope is -6/4.5=-4/3, so the equation is of the form y=-4x/3+c where c is the y intercept, which is 6, so y=-4x/3+6. Put y=3 and we get 4x/3=3 so x=9/4=2.25. That gives us f^-1(3)=2.25.