Respuesta :

26 = 2*13
12 = 2*6 

26*12 = 2*13 * 2*6 = 2(13*6) =2*78 =156

hope this will help you 
26*12

(2*13)*(2* 2* 3)

(2*2*2)*(3 * 13)

8 * 39

=  312