tolong kak kalau bisa pakai caranya

Pak Karto = 18 jam
Pak Darto = 12 jam
Bersama sama = ?

[tex] \frac{1}{ T^{a} } = \frac{1}{ T^{b} } + \frac{1}{ T^{c} }[/tex]
[tex] = \frac{1}{18} + \frac{1}{12}[/tex]
[tex] = \frac{2+3}{36}[/tex]
[tex]= \frac{5}{36}[/tex] Jam yakni [tex] \frac{36}{5} = 7 jam 12 menit