Question 829877
Find the average with S being the score on the last test which makes for a total of 7 tests. 
{{{(87+100+71+78+71+65+S)/7>=90}}}
{{{87+100+71+78+71+65+S>=630}}}
Now solve for {{{S}}}. 
If its less than or equal to 100, it's still possible.