Hi Nabeel, I used a bit of model or reimagining how it would work. The small part indicated as 15 is the most important. From there I minus 1/4 from 1/3 to get the difference. The difference represents the 15 fewer stamps. Then since marcus gave away 1/4, i convert 1/4 into 3/12. Since 3 units given away, I multiply by 3 to get 45. Hope this helps !