Stan's Skate Shop is having a sale on skateboards. The original price for its Extreme Skateboard was $84.50. The sale price for the skateboard is $50.70. What is the percent decrease in the price of the skateboard?

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