I know that this is a easy one but to me it is hard idk math lol 140/18

Ineed i do not understand i'm only 8

Could somebody me with this radical simplification?

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.