This fast food contains 20 grams of fat.

(2) Let the mass of the minerals contained be x grams, and the meaning of the question is: x+4x+20+400×40%=400.

∴x=44，

∴4x= 176

Answer: The mass of protein contained is176g.

(3) Solution 1: If the mass of minerals contained is y grams, the mass of carbohydrates contained is (380-5y) grams.

∴4y+(380-5y)≤400×85%，

∴y≥40，

∴380-5y≤ 180，

The maximum carbohydrate content is 180g.

Solution 2: Let the mass of minerals contained be grams, then n ≥ (1-85%-5%) × 400.

∴n≥40，

∴4n≥ 160，

∴400×85%-4n≤ 180，

The maximum carbohydrate content is 180g.