Problem 31)
The terms 10s and -8s are like terms. This is because they have the same variable term: s.
What we do is simply subtract the numbers in front of the letter s like so 10-8 = 2
So 10s - 8s = 2s
Think of it like this: we have 10 sodas and we take away 8 sodas. We'll be left with 2 sodas. Writing 10s-8s = 2s is a way to use shorthand.
So overall, the original expression 5 + 10s - 8s turns into 5 + 2s which is the final answer
Note: 5 + 2s can be written as 2s + 5. The order in which we add things up doesn't matter.
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Problem 37)
In this problem, the terms 5 and -7 are like terms. They are the terms without any variables (letters) attached to them.
If we have 5 dollars and we want to spend 7 dollars to buy something, then we'll be 2 dollars in debt. Use negative numbers to indicate debt.
So 5 - 7 = -2
The expression 5 + (4g - 7) simplifies to 4g - 2 which is the final answer
