We are given that the concentration of the KCl is 2 meq / mL. Assuming that the ampule also has exactly this concentration, therefore:
  
 amount of KCl in ampule = (2 meq / mL) * (20 mL)
 amount of KCl in ampule = 40 meq
  
 This amount of KCl is now inside a solution of 1 Liter (also equivalent to 1000 mL), therefore the new concentration in the resulting solution is:
 new concentration = 40 meq / 1000 mL
 new concentration = 0.04 meq / mL
  
 Since 0.04 in decimal is 4% in percentage, therefore the strength of the resulting solution is 4% KCl.