Jawabanmu

2014-06-02T16:44:48+07:00
1/f = 1/s + 1/s'
1/10 = 1/s + 1/8
1/s = 1/10 - 1/8
1/s = 4/40 - 5/ 40
1/s = -1/40
s = 40 cm