Pretty sure it would save OP more than just $400 a year. Apart from the gas saved, think about lesser wear and tear on the vehicle, fewer clothes to wash and they tend to last longer, skip shaving whenever WFH, sleep more because you don't have to get ready for work, get things done around home (not at the cost of office work, but surely helps), and finally the mental peace gained from not having to commute.
Our office has removed WFH recently while it was a nice option earlier. I used to allow myself one WFH per week to keep sanity (killed by commute) and to get things done that could only be done on weekdays, but now I am starting to feel frustrated. Time to move, maybe.