Answer is: 152 mL of 9% vinegar and 228 mL of 14% vinegar.
ω₁ = 9% ÷ 100% = 0.09.
ω₂ = 14% ÷ 100% = 0.14.
ω₃ = 12% ÷ 100% = 0.12.
V₁ = ?.
V₂ = ?.
V₃ = V₁ + V₂.
V₃ = 380 mL.
V₁ = 380 mL - V₂.
ω₁ · V₁ + ω₂ ·V₂ = ω₃ · V₃.
0.09 · (380 mL - V₂) + 0.14 · V₂ = 0.12 · 380 mL.
34.2 mL - 0.09V₂ + 0.14V₂ = 45.6 mL.
0.05V₂ = 11.4 mL.
V₂ = 11.4 mL ÷ 0.05.
V₂ = 228 mL.
V₁ = 380 mL - 228 mL.
V₁ = 152 mL.