I only see two red arrows, although I see three questions.
1) If you want ka to be defined numerically you must use the numeric assignment operator. You have ka followed by a boolean equals. Replace the boolean equals with a numeric assignment.
2) Symbolic math does not handle units. It mostly treats them as undefined variables.
3) No, you do not have that level of control over how the result is displayed.
As an additional note, you should be very careful with the use of the float keyword. It does not just change the precision of the displayed result, it changes the precision of the calculations. If you want to change the precision of the displayed result go to "Format", "Result", and on the "Number Format" tab check "Apply to symbolic results".
