Final answer:
To find the estimated sum using compatible numbers, round 6.6 to 7 and add it to 12 to get 19, which is approximately 18, the closest estimate given in the options.
Therefore, the correct answer is: option b) 18
Step-by-step explanation:
The question is asking for the estimated sum of two numbers using compatible numbers.
Compatible numbers are numbers that are easy to add mentally, often by rounding one or both numbers to a nearby mental milestone.
In the case of 6.6 and 12, a compatible number for 6.6 would be 7, since it is the nearest whole number.
Therefore, the estimated sum of 7 (rounded from 6.6) and 12 is 19.
But, as we are looking for the closest estimate given in the options, the best answer would be 18, which is option b) and considered a compatible number for 19 in this context.