the load L a horizontal beam can safely support various jointly at the with w and the square of the depth d and inversely as the length, therefore we have the next formula
[tex]L=k\frac{wd^2}{l}[/tex]In our case
l=10ft
w=4in
d=8in
L=960lbs
Then we substitute the values
[tex]960=k\frac{(4)(8)^2}{10}[/tex]Then we isolate the constant
[tex]k=\frac{960(10)}{(4)(8)^2}=37.5[/tex]Then for the other case
l=16ft
w=3.5in
d=5in
We substitute in the formula
[tex]L=37.5\frac{(3.5)(5)^2}{16}=205.08\text{lbs}\approx205[/tex]ANSWER
L=205 pounds