rank nation gold silver bronze total
rank
nation
gold
silver
bronze
total
number
number
number
number
number
number text number number number number
1 nigeria 13 5 6 24
what is the difference of silver medals between south africa and kenya ?
WP VBD-AUX DT NN IN NN NNS IN NNP NNP CC NNP .
7
select ( select c4_number from w where c2 = 'south africa' ) - ( select c4_number from w where c2 = 'kenya' )