The sum of three numbers is 2100. the first number x is equal to the sum of the other two (y and z) which are equal to each other. what are the three numbers x, y and z

We will have a system of equations, and we are going to solve it by using substitution.
Let's make the equations.
x+y+z=2100
z+y=x
Since y and z are equal, I think it is easier for us to have them as one variable for now. Let the value of z and y be a.
These are the equations now.
x+2a=2100
2a=x
Since the second equation is giving the value of x, let it replace the value of x also in the first equation.
2a+2a=2100
4a=2100
2100÷4= 525
so, x and y equal 525. Let's put this in our original equation.
x+525+525=2100
x+ 1,050= 2,100
x= 1,050
So, x=1,050, y= 525 =z.

The answer would be 16