Common communitive error write an equation that illustrates a common error students make when applying the communitive property​

What value of x is in the solution set of 4x - 12 s 16 + 8x? -10 -9 -8 -7

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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.