Let the total work to be done = 60 units Let rates at which Ram, Shyam and Hari alone do the job be $$x$$ , $$y$$ and $$z$$ units/day respectively. Rate at which Ram & Shyam completes the work = $$frac{60}{12}$$ = 5 => $$x + y = 5$$ Similarly, $$y + z = 4$$ and $$z + x = 3$$ Adding all the above equations, we get : => $$2(x + y + z) = 12$$ => $$x + y + z = 6$$ Substituting value of $$(y + z)$$ in above equation, we get $$x = 6-4 = 2$$ => No. of days required by Ram to finish the work = $$frac{60}{2}$$ = 30 days