"D. Increasing the concentration of reactants" would most likely affect the rate of a chemical reaction since the other options only affect the environment.
Hemoglobin
The protein inside (a) red blood cells that carries oxygen to cells and carbon dioxide to the lungs is (b) hemoglobin
-3(x - 3) = x + 9 - 4x
Firstly, before we simplify the whole thing altogether, let's simplify each respective side. Distribute accordingly on the left side (the number outside the parentheses is distributed to the numbers inside the parentheses), and we can add the numbers with variables together on the right side.
-3x + 9 = -3x + 9
Now, let's add 3x to both sides, to simplify both sides now. This leaves us with: 1, I believe, since -3 ÷ -3 is 1.
x = x, and since x also equals to 1, our answer is 1. And once you check, substituting 1 for x, you will find that 1 is the correct answer.
You can solve this by saying that there are 3 Cl for every 1 Al therefore a ratio of 1:3. If you have 12 Cl ions you can find how many Al ions there is
so (x)Al : 12 a unkown amount of Al ions gives you 12 Al ions from the ratio we know that we have 1 Al for 3 Cl therefore we can divide 12 by 3 to get the number of Al ions. The answer is 4 Al ions for 12 Cl ions.
Hope this helps :).