Ned pours 7 2/5 ounces of water from a beaker contains 10.25 ounces . How much water is left?

2/5 = 0.4 as a decimal.

Now subtract:

10.25 - 7.4 = 2.85 ounces are left

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value