The property that justifies this statement is known as the Transitive Property of Equality.
In mathematics, the Transitive Property states that if two values are equal to a third value, then they are equal to each other. In this case, if we have 3x equal to both 4 and 10, we can assert that 4 equals 10 based on their equal relation to 3x. Hence, we can also conclude that since 3x is equal to another expression that results in 6, it follows the same transitivity in terms of equality.
In simpler terms, if A = B and A = C, then B = C. Therefore, knowing that 3x = 4 and 4 = 10 allows us to deduce that there is a consistent value for 3x that also equals 6. This showcases how the Transitive Property allows us to link values through their common equality.