令a=1/x.b=1/y
则a+b=1/21 (1)
3a+5b=3/14 (2)
(1)×5-(2)
5a-3a=5/21-3/14
2a=1/42
a=1/84
b=1/21-a=1/28
所以
x=1/a=84
y=1/b=28