Question

Blue cassests hold 45 min. Of music

Answer 1

Let the number of Blue casset be b and that of green be g.
Thus the total number of cassets will be:
b+g=16
hence
g=16-b.......i

The total amount was:
45b+55g=830..ii
plugging i in ii we get:
45b+55(16-b)=830
45b+880-55b=830
simplifying 
45b-55b=830-880
-10b=-50
thus
b=5
hence
g=16-5=11
number of blue cassets was 5 and that of green was 11