720000/X=700000/（X-1000）
72/x=70/(x-1000)
72(x-1000)=70x
72x-72000=70x
72x-70x=72000
2x=72000
x=36000
s/(s-1000)=72/70
70s=72(s-1000)
70s=72s-72000
72s-70s=72000
2s=72000
s=36000