Answer:
Between 90 and 110 degrees
Step-by-step explanation:
Ideally, the angle should not be less than 90° so that your elbows could be parallel to the workstation. This will in turn mean that the shoulders will be relaxed and it will make it a lot less stressful to keep the wrists in a straight manner.
Looking at the options, there is no exact figure of 90°, however, it could be between 90° to 110° because the difference is not going to be much in terms of making the shoulders relaxed.