Missing question: volume of solution on the left is 10 mL.
V₁(solution) = 10 Ml.
c₁(solution) = 0.2 M.
V₂(solution) = ?.
c₂(solution) = 0.04 M.
c₁ - original concentration of the solution, before it gets diluted.
c₂ - final concentration of the solution, after dilution.
V₁ - volume to be diluted.
V₂ - final volume after dilution.
c₁ · V₁ = c₂ · V₂.
10 mL · 0.2 M = 0.04 M · V₂.
V₂(solution) = 10 mL · 0.2 M ÷ 0.04 M.
V₂(solution) = 50 mL.