Sallie earned a grade of exactly $90 \%$ for a marking period based on six equally weighed tests. The four test papers she can find have grades of exactly $83 \%$, $96 \%$, $81 \%$, and $82\%$. What is the sum of the percent scores of the two missing grades?
Suppose each test is worth $x$ points.  Then on the tests Sallie found, she has a total of $.83x + .96x + .81 x + .82x = 3.42 x$ points.  In all, she earned $6\cdot .9x = 5.4 x$ points.  Thus, on the two remaining tests she scored $1.98x$ points, which is a total of $\boxed{198\%}$.