Wyo. Stat. Ann. § 15-6-446

Extra work in connection with any local improvements not particularly provided for in the plans, specifications, estimates, bids and contracts shall be performed by the contractor at the direction of the city engineer at a cost of labor and materials plus fifteen percent (15%) for superintendence. The amount shall be included in the assessment for the improvement or be paid out of the general or road funds of the city or town in the discretion of the governing body.