Answer:
third number = 4,
equation of y, y = 5x - 11
equation of n, n = 4x
equation of x, n + x + y =19
Step-by-step explanation:
so lets write evertything as a n equation. n + x + y =19. N is the first number, x is the second number, and y is the third number. We will write the equation for y as follows 5x - 11. N will be four times the second number, so 4x. If substitute the values for out equation for x we will find what x equals to. So (4x) + x + (5x - 11) = 19
10x = 30
x = 3.
Then you substiute the answer for x in the equation for y. This will get you 5(3) - 11
15 - 11
4 = third number
They added it wrong. They added it like this:

When it shouldve been this:

They just added a place marker in all numbers below 100.