Northstar, an auto parts manufacturer, pays employees a higher hourly rate when they learn to operate more stages of the work process. Employees earn $$15$ per hour when they are hired, and they can earn up to $$30$ per hour if they master all $12$ areas$/$stages$.$ Which reward system are they using? Job analysis system Skill$-$based pay Piece$-$rate pay Seniority$-$based pay Gainsharing