SQLITE3 query condition

I'm new to sqlite3 and have hit a bit of a wall with my database. I don't really have anybody else to ask so a friend recommended I post here to try get a bit of help.

Say I have two tables

restaurants:

Restaurant  Location  Chef
'All Beef'  'London'  'Bob'
'All Lamb'  'Paris'   'Mike'
'All Pork'  'Berlin'  'Jill'
'All Veg'   'London'  'Heather'

chefs:

Name      Gender     Place_Of_Birth
'Bob'     'Male'     'London'
'Mike'    'Male'     'Paris'
'Jill'    'Female'   'London'
'Heather' 'Female'   'Berlin'

'How many restaurants are there in London with chefs that were not born there?'

Just looking for a point in the right direction, thanks a lot!