Explanation:
The given expression is :
[tex]\dfrac{w}{2}-12=18[/tex]
The value of w can be solved as follows :
Add 12 to both sides,
[tex]\dfrac{w}{2}-12+12=18+12\\\\\dfrac{w}{2}=30[/tex]
Cross multiplying, we get :
[tex]w=2\times 30\\\\w=60[/tex]
Leon should have made mistake at last step where instead of multiplying 2 and 30 he divides 30 by 2 so that he get 15 as answer.