You are given a math word problem and you are supposed to apply addition or subtraction mathematical operators on the numbers embedded in the text to answer the following question and then only report the final numerical answer.

Professor Ellison weighed 2 pieces of metal for an experiment . The piece of iron weighed 11.166666666666666 pounds and the piece of aluminum weighed 0.8333333333333334 pound . How much more did the piece of iron weigh than the piece of aluminum ?
10.333333333333334

There are 33 oak trees currently in the park . Park workers had to cut down 18 oak trees that were damaged . How many oak trees will be in the park when the workers are finished ?
15

Tim 's cat had kittens . He gave 3 to Jessica and 6 to Sara . He now has 9 kittens . How many kittens did he have to start with ?

18