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.

[EX Q]: Joan has 40 blue balloons Melanie has 41 blue balloons . How many blue balloons do they have in total ?
[EX A]: 81

[EX Q]: 29 birds were sitting in a tree . Some more fly up to the tree . Then there were 42 birds in the tree . How many more flew up to the tree ?
[EX A]: 13

[EX Q]: A pet store had 38 siamese cats and 25 house cats . During a sale they sold 45 cats . How many cats do they have left ?
[EX A]:
18