Someone stole 100 bucks from a store, he comeback and buy an something that cost $70 and pay with $100 he stole earlier, the store's owner gave him 30 bucks back as change.
how much money the store lost?

List x1, x2, x3, x4 where xi is the left endpoint of the four equal intervals used to estimate the area under the curve of f(x) between x = 4 and x = 6. a 4, 4.5, 5, 5.5 b 4.5, 5, 5.5, 6 c 4.25, 4.75, 5.25, 5.75 d 4, 4.2, 5.4, 6