sistem persamaan linear tiga variable. tolong ya .....

Andi dan Budi = 12 menit
1/A + 1/B = 1/12

Budi dan Candra = 15 menit
1/B + 1/C = 1/15

Andi dan Candra = 20 menit
1/A + 1/C = 1/20

Jumlahkan
(1/A + 1/B) + (1/B + 1/C) + (1/A + 1/C) = 1/12 + 1/15 + 1/20
2/A + 2/B + 2/C = (5 + 4 + 3)/60
2(1/A + 1/B + 1/C) = 12/60
1/A + 1/B + 1/C = 6/60 = 1/10

Andi, Budi dan Candra = t menit
1/A + 1/B + 1/C = 1/t
1/10 = 1/t
t = 10 menit