Final answer:
Harold Blair was a singer and aboriginal activist known for his voice and advocacy. The letter to the Prime Minister was dated May 10, 1967. Its influence would depend on various factors and cannot be determined without more context.
Step-by-step explanation:
Harold Blair was a singer and an aboriginal activist. He was known for his powerful voice and his work in advocating for the rights of Indigenous Australians. As a talented singer, Blair used his platform to raise awareness of the issues faced by the Aboriginal community in Australia.
The date of the letter to the Prime Minister mentioned in the question is May 10, 1967.
Regarding the writer's offer and whether it suggests that the government was not campaigning hard enough for the referendum, we do not have enough context to determine the exact nature of the offer or the motivation behind it. However, it is possible that the writer made the offer to support and strengthen the government's campaign for the referendum, rather than suggesting that the government was not campaigning hard enough.
As for its influence, the letter's impact would depend on various factors such as the reasons behind the writer's offer, the content of the letter, and the response of the Prime Minister and government officials. Without further information, it is difficult to determine the letter's overall influence.