We are working on expressions, equations and inequalities with all of the operations. The rule we follow to know which operation to do first is called the Order of Operations.
It goes like this:
Multiply and/or divide (left to right)
Add and/or subtract (left to right)
We use the Mnemonic Device to help us remember the Order of Operations.
Example: 45 - (3 x 8) + 9
In this expression we would multiply 3 x 8 first because it is in parentheses.
That would leave us with 45 - 24 + 9
Then we subtract because it come first moving from left to right.
That would leave us with 21 + 9 which equals 30.
So the value of 45 - (3 x 8) + 9 is 30.