I think in this case it is just to differentiate from the word קרירה, the feminine form of "cool, moderately cold".
Why the lamed in front of career. How do you get "for" out of it? I got it right because I peeked at the hint, but I would never guess this if I had to do it from English to Hebrew. I may have put זה טוב בשביל הקריירה שלי
Translating prepositions is not straight forward, unfortunately. English "for" can be בשביל, ל, למען, and probably others. I think the best way to grasp it is to practice and have a hunch for it over time.
See in this exercise the masculine form of "good" is used for "I have a good career", and in a prior exercise you used a feminine version of "Good"for "He has a good career". Why are there inconsistencies?
I know Zeh is for masculine. My question was there is an inconsistency with a prior exercise which used "Tova" instead of "Tov" when it stated "He has a GOOD career". The word "GOOD" should have likewise been in the masculine form.