Explanation:
z = (specific score - mean) / standard deviation
in our case
z = (80 - 70)/6 = 10/6 = 5/3 = 1.666666... ≈ 1.67
as most z-tables round the z-scores to hundredths.
not to forget : the sign matters. so, don't worry, if you have e.g. a specific score of 60 :
(60 - 70)/6 = -10/6 = -5/3 = -1.666666... ≈ -1.67
you did not do anything wrong. that is all ok and valid.