Apply the rules for order of operations to simplify 2 + 3 − 4 + (5 × 4). a. 9 b. 22 c. 24 d. 21

Order of operations is easy to remember using the acronym PEMDAS. I always learned to remember the phrase "Please Excuse My Dear Aunt Sally" as a tool.

P - stands for parentheses. Always do your operations inside parentheses FIRST!
E - stands for exponents. Figure out the value of your numbers with exponents next.
M - multiplication  Any multiplication in your problem would be your third step.
D - division  Same thing for this one. Any dividing in the problem is done in this step
A - addition
and
S - subtraction

So for this specific problem: 

2 + 3 - 4 + (5 x 4)

You see the parentheses and take care of them first:

2 + 3 - 4 + 20

There are no exponents so we skip E in this one, and you took care of all the multiplication in the problem in step one. There is no division. So now all you have left is your last two steps.

Now another thing you need to remember is that the last two steps kind of go in pairs with each other. Multiplication with division and addition with subtraction. So when you reach your Addition step you're going to start at the farthest left point in your equation and work right from there solving both addition and subtraction as you go along.

2 + 3 - 4 + 20

First, add 2 and 3 to get 5.

5 - 4 + 20

Next, subtract 4 from 5 and get 1.

1 + 20

I'm sure you can figure it out from there :)

Hope this helped you!!