We solve equations by the method of graphing or by solving.
The method of solution is our choice. Graphing helps our visual grasp. But accuracy requires solving of the equations.
The linear equations of one variable does not require substitution or elimination. We solve linear equation of one variable and one single equation by isolation of the unknown or variable to one side and knowns or numbers to the other side. The type of operations we do is (i) adding or subtracting equals to both sides, (ii) multiplying or dividing both sides by equals. But never multiply or divide by zeros thinking that zeros are equals.
In solving equations with two or more variables we are dealing with more than one equations. Here we can use the technic of reducing the number of variables and the number of equtions either by elimination or substitution till we arrive at a single equation with a single variable.