P(x) = -x 3 + x 2 - 60x + 100, x ≥ 5 is an approximation to the total profit (in thousands of dollars) from the sale of x hundred thousand tires. find the number of tires that must be sold to maximize profit.

Lizette is training for a marathon. at 7: 00 she left her house and ran until 8: 30, then she walked until 11: 30. she covered a total distance of 18 miles. her running speed was six miles per hour faster than her walking speed. find her running and walking speeds in miles per hour.