2/7 are covered
so, 5/7 are uncovered
now,
let no. of covered be x
no. of uncovered=15000
(5/7)/(2/7)=15000/x
5/2=15000/x
5x=15000×2
x=15000×2/5
x=3000×2
x=6000
so, 6000 are covered
now,
total spectator
=15000+6000
=21000
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