14.
Let's say 'x' represents your first dog and 'y' represents your 2nd dog.
You know that x = 5 ft long. You also know that x = 4/5y. So let's plug in 5 for 'x' in the 2nd equation and solve for 'y'.
5 = 4/5y
Divide 4/5 to both sides or multiply by its reciprocal, 5/4.
6.25 = y
So your 2nd dog is 6 1/4 ft long.
15.
You would typically use ounces to measure the amount of juice in a glass. The other measurements are too large.