Did Watt work as a mathematical- instrument maker from the age of 19? (общий)
Watt worked as a mathematical- instrument maker from the age of 19, didn't he? (разделит.)
Who worked as a mathematical- instrument maker from the age of 19? (вопр. к подлежащ.)
When did Watt start working as a mathematical- instrument maker? (спец.)
Watt worked as a mathematical- instrument maker or an engineer? (альтернат.)