Answer is: 180 grams of 2.5% "h" cream should be mixed.
ω₁ = 2.5% ÷ 100% = 0.025.
ω₂ = 0.25% ÷ 100% = 0.0025.
ω₃ = 1% ÷ 100% = 0.01.
m₂ = 360 g.
m₃ = m₁ + 360 g.
m₁ = ?.
ω₁ · m₁ + ω₂ · m₂ = ω₃ · m₃.
0.025 · m₁ + 0.0025 · 360 g = 0.01 · (m₁ + 360 g).
0.025 · m₁ + 0.9 g = 0.01 · m₁ + 3.6 g.
0.015 · m₁ = 2.7 g.
m₁ = 180 g.
