1) 5 = 2t - s

Question

1) 5 = 2t - s
   20 = 8t - 4s
Answer: Identity

2) 4t - 6s = 2
  -6t + 9s = -3
Answer Identity

drwls · Answer

In both cases, the equations are not independent. If the first equation is correct, the second must be also.