The first step to solving this is understanding all of the important information and disregarding useless information. By doing this, we can see that we are looking for what 25% of 12 is.
The next step is setting up the expression and solving. To solve for a percent, we should multiply the number by the percent's decimal value, which is the percent placed over 100. In this case, the percent's decimal value is .25, so the expression would be set as:
=12*.25
=3
Therefore, we know there are 3 grams of copper for 12 grams of brass.
