Substitute the solutions of the solved unknowns into the left and right of the original equation respectively. If left equals right, then the solution of the unknown quantity is the solution of the original equation.

For example: 2x+5=7

2x=7-5

x= 1

Test: Left =2× 1+5=7.

Right =7

Left = right

So: x= 1 is the solution of the meta-equation.