Answer:
Megan added 4 rocks.
Explanation:
We know this because if the box had 8 rocks in it intially and it now has 12 rocks, we know that Megan added 4 rocks. Since, 8+4= 12 or 12-8=4
Equation form:
r = how many rocks Megan added
8+r=12
12-8=4
r=4
Megan added 4 rocks.
Hopefully this helps!! ^^