Total playing time for all 30 is 30*42 = 1260 minutes
Total playing time for 25 left is $${\mathtt{25}}{\mathtt{\,\times\,}}{\mathtt{42.8}} = {\mathtt{1\,070}}$$
Total playing time for the 5 gone is $${\mathtt{1\,260}}{\mathtt{\,-\,}}{\mathtt{1\,070}} = {\mathtt{190}}$$
Average playing time for the 5 is $${\frac{{\mathtt{190}}}{{\mathtt{5}}}} = {\mathtt{38}}$$ minutes