1) suppose that s/a=5.0 and n/s=.08. solve for n/a

2) suppose a-d=e, that n=20000, e/a=.75 and n/e=.40. compute d/a

3) assume that s/a=6.5, d/a=.40, n/e=.75 and a=d+e. solve for n/s