Final answer:
To add 659.98 ft² and 28.07 ft with the correct number of significant digits, the answer is 688.05 ft², rounded to 2 decimal places.
Step-by-step explanation:
To add the numbers 659.98 ft² and 28.07 ft with the correct number of significant digits, we need to consider the number with the least number of decimal places, which is 28.07 ft with 2 decimal places.
Because the number with the least decimal places has 2 decimal places, we need to round the final answer to 2 decimal places as well.
Adding the numbers gives us 688.05 ft². Rounding to 2 decimal places, the answer is 688.05 ft².