20p+22p-12p=90 as all of the terms on the left are 'p's then we consider them to be called like terms. When we have like terms we can add or subtract freely. so: 20p+22p-12p=90 20p+22p=42p 42p-12p=30p therefore we get: 30p=90 this is the same as 30*p=90 to find do we need to 'work backwards' to move the 30 to be with 90. So to 'work backwards' we do the opposite of multiply and divide it instead to both sides of the equation. 30/30*p=90/30 p=90/30 p= 3
