Let the total sum of the scores of the first class of 35 students be
a. The mean is 74.3
.
So

Also, let the total sum of the scores of the second class of 28 students be
b. The mean is 67.6 .
so

The combined group has 35+28=63 students. The sum of their scores is
a+b=2600.5+1892.8=4493.3
Thus, the mean of the combined group is
