Substitution method
y = x + 3 (*)
y = 3x + 1 (**)
Substitute (*) to (**):
3x + 1 = x + 3 subtract 1 from both sides
3x = x + 2 subtract x from both sides
2x = 2 divide both sides by 2
x = 1
Put the value of x to (*):
y = 1 + 3
y = 4
Answer: x = 1 and y = 4 → (1, 4).
