If I'm understanding this correctly:
Tiger consumes 18lb/day of food. If we want to calculate how much is consumed in 28 days, assuming that rate is consistent, the answer is 18*28 = 504lb of food.
Reduce each ratio to its minimum expression to find if they are equal.
35:28

10:8

Since both ratios reduce to 5:4, they are equivalent.
Another way to check a:b is equivalent to c:d, is that a*d = b*c
In this case, this will be true if 35 times 8 is equal to 10 times 28:

Since both products are equal, then the ratios are equivalent.