15 tons of coal were brought to the coal warehouse on three machines. The mass of coal on the first machine

15 tons of coal were brought to the coal warehouse on three machines. The mass of coal on the first machine is equal to the mass of coal on the second machine. The mass of coal on the third is 1.5 tons more than on the first. How many tons did you bring in the third car?

Let the mass of coal in the first machine be x tons, then x tons were also brought on the second machine, and (x + 1.5) tons of coal were brought on the third. It is known that a total of 15 tons of coal were brought to the warehouse. Hence, we get:
x + x + x + 1.5 = 15;
3x = 13.5;
x = 4.5.
That is, the first car brought 4.5 tons of coal.
The third car brought 4.5 + 1.5 = 6 tons of coal.
Answer: the mass of coal brought in by the third vehicle was 6 tons.