Compare the divisor x+1 to the linear polynomial x−a. If x+1=x−a, what is a equal to? Enter your answer as a number, like this: 42

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.