When hydrolysis of tristearate fat in an amount of 5 mol, stearic acid was obtained in mass.

Let’s determine the molar masses of substances:
M (tristarate) = 806 g / mol;
M (Stearin. K-you) = 284 g / mol;
Let’s make the proportion:
5 mol (tristarate) – X mol (stearin. To-you);
1 mol -3 mol from here, H. mol (stearin. To-you) = 5 * 3/1 = 15 mol;
Let’s calculate the mass of stearic acid:
m (stearin.k-you) = Y * M = 15 * 284 = 4260 g.
Answer: the mass of stearic acid is 4260 g.