You do it because if you added before you multiplied your answer would be way out in the atmosphere. I'm not sure who invented that though...
multiply first, and then add
you are suppose to MULTIPLY on area.
You multiply.
multiply
you can multiply 281 and 3 you can add 840 and 3
multiply first, and then add
you are suppose to MULTIPLY on area.
You multiply.
multiply
multiply
Multiply for the area, add for the perimeter.
you can multiply 281 and 3 you can add 840 and 3
Add.
you add
You multiply them.
multiply
The numbers that multiply to 72 and add to -17 are -8 and -9. When you multiply -8 and -9, you get 72, and when you add them together, you get -17.