How many grams of lactic acid are in 1 liter of lactic acid?

The question is missing the concentration of the lactic acid solution. You also need the molar mass of the lactic acid (or its molecular formula to calculate it)

For example, the question should read how many grams of lactic acid (C3H6O3) are in 1 liter of 0.5 M solution of lactic acid?

Now I can teach you how to calculate the mass in grams of lactic acid.

1) number of moles, n

M = n / V = > n = M*V = 0.5 M * 1 l = 0.5 moles

2) molar mass of C3H6O3

C3H6O3: 3 * 12g/mol + 6 * 1g/mol + 3*16g/mol = 90 g/mol

3) mass in grams = number of moles * molar mass

mass in grams = 0.5 mol * 90 g/mol = 45 g

Answer: 45 g