The answer to your problem is a+6x+5.
The simplified ratio is 2:3. Since the smaller number when it's not simplified is 18, let's divide 18 by 2 to get our factor.
18/2 = 9.
So we can multiply 9 by 3 to get the missing larger number.
9 x 3 = 27.
Your missing number is 27, hope this helps!

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Step-by-step explanation:
x = number
3x - 15 = (x - 12)×-4 or (12-x)×-4
3x - 15 = -4x + 48 or -48 + 4x
7x = 63, x = 9 or
33 = x