请教PREP数学题

129.
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If t is a positive integer and r is the remainder when t² + 5t + 6 is divided by 7, what is the value of r ?

(1) When t is divided by 7, the remainder is 6.

(2) When t² is divided by 7, the remainder is

请问这道题该怎么做啊，我完全没得思路。答案是A

谢谢各位了

昨天也回答了这个题目

(1) t=7a+6 然后t² + 5t + 6 =49a^2+84a+36+35a+30+6
            只有72不能被7除 余2

(2) t^2=7b+1
                只能推出t² + 5t + 6 =7b+5t+7 但不知道t是多少 所以不一定