You could either use the propotional method or unitary method, but I am going to be using the porpotional method since it is more quick.
Step 1
So first we would convert the numbers givin into a fraction by putting 5 over 140 and 20 over x which is the question mark.
Step 2
Then we would cross multiply, so multiply numbers that are diagonal to each other .140 would multiply with 20 and 5 would multiply with x.
Step 3
After we multiply (we do not multiply 5 with anything so it is just 5)we would have the equation , x times 5=2800. Since we need to isolate x we would take 5 and put it under 2800 so it would be 2800 divided by 5.
Step 4
After we divide 2800 by 5 we would have 560 which equals to x , making it the ounces needed to feed 20 animals at the shelter .
Summarise
To briefly explain this the way to find the answer would be 20x40 divided by 5.
Hope this helped :D