Answer: 5x+27
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Work Shown:
15 and 12 are one pair of like terms that add to 15+12 = 27
The other pair of like terms are -5x and 10x which combine to -5x+10x = 5x
you can think of it as 10x-5x = 5x, or another way is
10x = 10 boxes
5x = 5x boxes
10x-5x = start with 10 boxes, take away 5 boxes ---> 5 boxes left over
after combining the like terms, you'll end up with 5x+27
