Find the number of authors of the paper 'Vehicle Velocity Observer Design Using 6-D IMU and Multiple-Observer Approach'.
The paper 'Vehicle Velocity Observer Design Using 6-D IMU and Multiple-Observer Approach' has how many authors?
SELECT ?answer WHERE { <https://dblp.org/rec/journals/tits/OhC12> <https://dblp.org/rdf/schema#numberOfCreators> ?answer }
<https://dblp.org/rec/journals/tits/OhC12>