When a performance bond incorporates another contract by reference, the contracts must be construed together using the principles of interpreting a surety contract: strictly in favor of the surety.Commercial Cas. Ins. Co. of Georgia v. Maritime Trade Center Builders, 257 Ga. App. 779, 783 (2002). Therefore, because the construction contract is incorporated into the performance bond, for the same reasons discussed above, plaintiffs are obligated only to DCBE.