设abc是实数，3a,4b,5c成等比数列，且1/a,1/b,1/c成等差数列，求a/c+c/a的值

3a,4b,5c成等比数列;
(4b)²=3a*5c;
ac=16/15b²;
1/a,1/b,1/c成等差数列;
1/a+1/c=2/b;
a+c/ac=2/b;
a+c/(16/15)b²=2/b
a+c=32/15