**Answer:**

The correct answer is D) 7+(3+1)=(7+3)+1

**Step-by-step explanation:**

The associative property of addition states that it doesn't matter how you group numbers inside of parenthesis, it gives you the same answer. So even though the groupings are different in that example, the answer is still the same.

The 15 lbs at $7=$105

So multiple 5x9 as a test and check results. 105-45=60

Here you can see that 60 is a factor of 6 by 10 so you got lucky and got the answer of 10lbs at $6 & 5lbs at $9=15 lbs at $7 average

X1 = 2.33333333333

x2 = <span>2.30952380952</span>

x3 = 2.30940108002