If Mary bought 12 of the Brand X batteries, how many of them lasted less than 15 hours? (Please show how you calculated this to get your answer)

Someone this asap for a group of students attends a basketball game. * the group buys x hot dogs at the concession stand for $2 each. * the group buys y drinks at the concession stand for $3 each. the group buys 29 items at the concession stand for a total of $70. how many hot dogs did the group buy?