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.

[Q]: Karen has 639 crayons . Cindy has 504 crayons . How many more crayons does Karen have than Cindy ?
[A]: 135


[Q]: Craig walked 0.2 mile from school to David 's house and 0.7 mile from David 's house to his own house . How many miles did Craig walk in all ?
[A]: 0.9


[Q]: Keith found 6 seashells , Jessica found 8 seashells , and Tim found 7 seashells on the beach . When they cleaned them , they discovered that 3 were cracked . How many seashells did they find together ?
[A]:
21