B. Reflection. Hope it helps you
Do the rainbow method
x^2 - 6x + 2x - 12
Now simplify
x^2 - 4x - 12
The answer is x^2-4x-12
The answer is the first one!
To solve for x, you undo what was done to x. The variable x is ...
- multiplied by y
- added to z
You "undo" these operations in the reverse order, so first we undo the addition of z. We accomplish that by adding the opposite of z:
... -10 -z = xy
Now, we undo the multiplication by y. We accomplish that by multipying by the reciprocal of y.
... (-10 -z)/y = x
We can rearrange this, if you like.
And, if you want, you can factor out the minus sign.
Notice that 45 hours is 3 times the half-life of 15 hours.
After the first 15 hours, 450 g decays to half this amount, 225 g.
After the next 15 (total 30), 225 g decays to 112.5 g.
After the next 15 (total 45), 112.5 g decays to 56.25 g.