by ambidex on Wed Aug 10, 2011 7:46 pm
If that's the exact question, then you're supposed to evaluate it.
If the question were 8 + 40 - 5(3 + 7), you'd know what to do, because all you have is numbers. You'd follow PEMDAS, do 3 + 7, then multiply by 5, then subtract your answer from 40 and then add 8. That would look like: 8 + 40 - 5 (11) = 8 + 40 - 55 = 8 -15 = -7.
When you don't just have numbers, like in the problem you've specified, you have to know how to deal with variables. "r" is a variable in your problem. What you're going to do is find all of the "r" numbers and do "math" with those numbers. This what is called "combining like terms." However, you'll find that "3r" is kind of stuck so what you need to do is use the distributive property to get it "unstuck". Here's what that'll look like: 8r + 40 - 5*3r + 5*7. Keep going: 8r + 40 - 15r + 35. Now you just have two r numbers and two normal numbers. Let's rearrange them: 8r - 15r + 40 + 35.
This isn't the final answer, but I hope you can find your final answer from here!