To find the answer we have to slowly analyze the command.
For surely on the one side we want to have total cash spent, so 80.8$
We know that there are 2 types of frames 5,80$ and 9.60$.
We know too, that f is the number of frames 5.80$ bought.
Simply, to find the cash spent on those frames we have to just mulitply 5.80$ times f, so we obtain [tex]f*5.8[/tex].
We can say that number of bigger frames is 20-f.
So to find cash spent on bigger frames we have to multiply 9.60$ times (20-f), so
[tex]9.60*(20-f)[/tex]
Now we can just add cost of all frames together
[tex]f*5.80+9.60(20-f)[/tex]
And we know that is equal to 80.8, so
[tex]f*5.80+9.60(20-f)[/tex]=80.8
As we can see, the answer is b.