To do this problem, you need to first get rid of all the parenthesis. Since all the operations are addition (+), remember the <span>Associative Property of Addition. This property says when you're adding, it doesn't matter where you put the parentheses because it'll all add up to the same thing.
That means </span>(3b + 2r) + (4b + r) = (3b + 4b) + (2r + r), or even, just get rid of the paratheses in general and have (3b + 2r) + (4b + r) = (3b + 2r + 4b + r).
Either way, now you can add like terms so: (3b + 2r) + (4b + r) = (3b + 4b) + (2r + r) = 7b + 3r
The slope of a line is the ratio of the change in y to the change in x. The slope of the given line is 1/2 = -6/-12. That is, when y changes by -6 to go from 6 to zero, x will change by -12 to go from 0 to -12.