Let the highest score be x, and when the scores of the other two people are (X- 1) and (X-2) respectively, x is the smallest.
68+X+(X- 1)+(X-2)=324
X=86.3, but x is an integer. When x takes 86, 86+85+84+68=323.
When x takes 87, 87+85+84+68=324, which is the same as.
So x is at least 87.