Lets take an example to understand the Substitution method for solving a pair of linear equations:

2x + 3y = -4  …(1)
3x + y = 1    …(2)

Step – I  From either of the equations, find the value of one variable in terms of   other. eg. (2) implies

y = 1 – 3x    …(3)

Step – II  Put this value of y in the other equation (1).

2x + 3(1 – 3x) = -4
x = 1

Step – III  Put the value of x in equation (3)

y = 1 – 3(1) = -2