Question 856739
1/(2s)+1/s=1/7
1/(2s)+2/(2s)=1/7
3/(2s)=1/7
21/14s=2/14

a=2s=21

s=10.5
1/10.5+1/21=1/7
2/21+1/21=1/7
3/21=1/7
ok