Say you're trying to figure out what percentage 3 is of 15.
3/15 = x/100
You would cross multiply so..
3(100) = 15x
Then simplify.
300 = 15x
300/15 = 15x/15
20 = x
Therefore, 3 is 20% of 15.
A sequence of operations that will get you to the solution is ...
... d. multiply each side by-5, add 25 to each side
_____
That is not the only correct sequence of operations. However the other ones listed here are incorrect ways to get to x = -10.
You can do whatever multiplication and addition you like to each side of the equation, but if those operations are poorly chosen, they will make finding the solution more difficult.
