Answer:
49 stones
Explanation:
Write the following proportion based on the given ratio of marbles (m) to stones (s), and naming the unknown number of stones to find, with the letter "X":
6 m / 7 s = 42 m / X s
cross multiply to get the unknown in the numerator:
6 * X = 42 * 7
divide both sides by 6 to isolate X entirely on the left of the equal sign
X = ( 42 * 7 ) / 6
X = 49
Therefore, there are 49 stones