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.

At the beach , Miki and her sister both built sandcastles and then measured their heights . Miki 's sandcastle was 0.8333333333333334 foot tall and her sister 's was 0.5 foot tall . How much taller was Miki 's sandcastle than her sister 's ?
0.3333333333333333

A waiter at ' The Greasy Spoon ' restaurant had 29 customers to wait on . During the lunch rush he added another 20 customers . If 34 of the customers did n't leave him a tip , how many customers did leave a tip ?
15

A toy store had 5 giant stuffed bears in stock when they got another shipment with 7 bears in it . The put the bears onto shelves with 6 on each shelf . How many shelves did they use ?

2