Answer: 12
Step-by-step explanation:
Multiply 0.66666667 with 18 to get
0.66666667*18 = 12.00000006
The 6 at the very end is due to rounding error. In reality the 6's in 0.66666667 should go on forever. That 7 is from rounding up.
Anyways, the result 12.00000006 should be 12 exactly.
Note how
12/18 = 0.66666667
when using a calculator.