Machine R and machine S work at their respective constant rates. How a much time does it take machine R, working alone, to complete a certain job?
(1) The amount of time that it takes machine S, working alone, to complete the job is $${\frac{3}{4}}$$ the amount of time that it takes machin R, working alone, to complete the job
(2)Machine R and machine S, working together, take 12 minutes to complete the job