I get C, but somehow calculating further (which is not required in GMAT i m getting number of tests as a fraction )

Let's take X as total number of exams
Let S be the sum of marks excluding the last exams and the lowest score of 8
(1) (8+sum)/(x-1) =85........... insuff
EDIT!! (2)8+sum+95)/x=86.7........insuff ...this eqn was error!

(1) +(2) gives us 2 eqn in 2 variables therefore should be sifficient giving answer C

Edit!! Ans: B same as scoobydooby as the second eqn gives :(85*(x-1)+95*1)/X = 86.7

I get B

lets consider the group mean formula,
1st set has all the scores except the last one (say n scores)
2nd set has the last score only say x

applying group mean formula: (85n+1x)/n+1=86.7, to find n+1

Stmnt 1: lowest score is 8. not sufficient, as we have to unknows n and x
Stmnt 2: we know x=95, we can solve the group mean equation to get n+1, sufficient

(B)

85x+95 = (x+1)*87.6

x=5

so he took total 6 tests.