-9
There are the same signs so you'd just add them together and use whatever sign they are..
Multiply the equation:

The solution set is the same, because multiplying both sides of an equation by a non-zero number doesn't change the solution set. In fact, if you rewrite the equation as

Multiplying this by 3 (or whatever number, for all it matters) gives

Now, a product is zero if and only if at least one of the factor is zero. So, either
or 
Since the first is clearly impossible, the second one must be true, which is the original equation.
Answer:
3 + 1(3) +3 (the dollar amounts)
3+3+3
9
0.5 + 0.1 +0.1 +0.1 +0.5 (the cents)
1.3
9 +1.3 = 10.30 worth of groceries using front end estimation
Answer:
Denpeds on the left hand side of nagetive of the inequality sign
Y = 2/3x - 6
-2/3x + y = -6...multiply everything by -3
2x - 3y = 18 <== standard form