Describe how substitution works and give an example?

Substitution is a method used in mathematics and programming where one variable or expression is replaced with another equivalent value or expression. For example, in the equation ( y = 2x + 3 ), if we know ( x = 4 ), we can substitute 4 for ( x ) to find ( y ): ( y = 2(4) + 3 = 8 + 3 = 11 ). In programming, if a variable a holds the value 5, substituting a in an expression like a + 2 would yield 7.