Anumber, x, is 11 less than 3 times a smaller number, y,. the sum of the numbers is 24. solve for x and y

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.