JAG, LLC a General contractor won a bid to renovate schools in Boston. JAG subcontractred with REI Design Inc to supply windows for project. Under the subcontract, a company called River Run Window installers, Inc. was designated to install the windows. The subcontract provided that REI Design and River Run Windows would perform and complete the subcontract work together. The subcontract also specificially acknowledge that REI Design proposed to work in partnership with River Run installers. After completion of the project, a dispute over payment and the quality of workmanship arose between the parties. JAG claimed that REI and River Run should be jointly and severally liable for any liability found against either party, beacause the two were parterns in the window installation project. Was JAG correct? Why or Why not ?

Could you give me a lots of explanation, thank you!