We start by calculating the cooking loss, that is 25%.
Then, this loss is:
[tex]20\text{ oz}\cdot\frac{25}{100}=5\text{ oz}[/tex]Then, we are left with 20 - 5 = 15 oz.
43% of the 20 oz is not edible (fat and bones), so we can calculate this as:
[tex]20\text{ oz}\cdot\frac{43}{100}=8.6\text{ oz}[/tex]Then, what is left for eating is the original weigth less both losses:
[tex]20-5-8.6=6.4\text{ oz}[/tex]Is left for eating 6.4 oz.