Pareto efficency for perfect substitutes

[nikhita13]

Consider the following data:
  u1(x1,y1)=2x1+y1, ω1=(0,1)
  u2(x2,y2)=x2+2y2, ω2=(1,0)
How much will individual 1 consume in a Pareto efficient allocation that offers individual 1 a satisfaction level of u1=2.5?