Which equation below illustrates the associative property of addition? \left(2+8\right)+\left(1+9\right)=\ left(8+2\right)+\left(9+1\right)(2+ 8)+(1+9)=(8+2)+(9+1)
5\left(2+7\right)=10+355(2+7)=10+35
5+2\left(3+4\right)=5+6+85+2(3+4)=5 +6+8
\left(3+7\right)+2=3+\left(7+2\righ t)(3+7)+2=3+(7+2)

Suppose you are an avid reader and are looking to save money on the cost of books instead of paying about $20 for each book, you decide to look into purchasing a kindle for $120 you can purchase e-books for about $5 each 1. find the slope-intercept equation for the cost of the hard copy of books using x to represent the number of books 2. find the slope-intercept equation for the cost of the kindle with cost of e-books using x to represent the number of books