Answer:
The original equation is:
4.2 + z = 16.5
By substituting z with 12.3, Lainey can rewrite the equation as:
4.2 + 12.3 = 16.5
Now, Lainey can simplify the equation:
16.5 = 16.5
Since the left side of the equation equals the right side, the equation is balanced and both sides are equal. This confirms that Lainey's solution of z = 12.3 is correct.
By using the substitution property of equality and substituting the value back into the original equation, Lainey was able to check her solution and verify its accuracy.