Arkansas does not allow local jurisdictions like cities or counties to collect a local sales tax. The Arkansas state sales tax of 6.5% is applicable statewide. You can view the sales tax rates for various cities in Arkansas here.
Equitable adjustment is a term of art that includes an adjustment to fee, and the target. minimum, and maximum fees should not be increased in this case for what I hope are obvious reasons. The adjustment should be limited to the effect of the new wage determination on wages and fringes.
It is settled contract law that a contractor is entitled to an equitable adjustment under the changes article for the increased costs of performance due to defective specifications. Johnson & Son Erectors, ASBCA No. 24564, 81-1 BCA 15,082; Hol-Gar Mfg. Corp. v. United States, 175 Ct. Cl.