Respuesta :

15 = 3 - (z+6)
15 = 3 - z - 6
z = 3 - 6 - 15
z = -18

check:
15 = 3 - (z+6)
15 = 3 - (-18+6)
15 = 3 - (-12)
15 = 3 + 12
15 = 15 (true)
crisforp

So, 15 = 3 - z - 6   /  + z;

15 + z = 3 - 6 ;

15 + z = -3   /  -15;

z = -18;

Check the solution: 3 - (-18 + 6 ) = 3 - (-12) = 3 + 12 = 15. Okay!