He usually goes to work ()a car

in

by

参考
Mr. Wagle goes to work by a bus. One day he falls asleep
when the bus still has twice as far to go as it has already
gone.

Halfway through the trip he wakes up as the bus bounces over
some bad potholes. When he finally falls asleep again, the
bus still has half the distance to go that it has already
travelled. Fortunately, Mr. Wagle wakes up at the end of his
trip.

What portion of the total trip did Mr. Wagle sleep?

He usually goes to work 【in】a car

go to work by car ----是固定的用法
by = 凭借着什么交通工具的介词
又例如：She goes to work by bus every day.
但有“a”在交通工具前面是就不是用by

in
楼上的答案不对，用By的话应是by car中间什么也不加

对，用in