Final answer:
The correct written form of the number 64 is 'Sixty-four,' indicated by option (A). This adheres to the standard rule of using a hyphen to connect the tens and ones place in written numbers.
Step-by-step explanation:
The correct way to write the number 64 in words is Sixty-four. Therefore, the correct answer is (A) Sixty-four. When writing numbers in words, hyphens are used to connect the tens place and the ones place, as in sixty-four. Neither of the other options provided adheres to this standard written form for numbers.