Explanation:
Denominator =X
Numerator = X-12
Fraction = (X-12)/X
⇛(X-12)/X = 3/5
⇛5(X-12) = 3X
⇛5X-60 = 3X
⇛5X-3X = 60
⇛2X = 60
⇛X = 60/2
⇛X = 30
Denominator = 30
Numerator = 30-12 = 18
The fraction before simplified = 18/30
Please let me know if you have any other questions.