Hi @Hamidaafrinheart,
The answer would be

In this problem we are being asked to determine the t shirts that Nathan needs to sell to get a bonus.
To solve this we simply need to add and subtract.

Now, subtract this number from 75 to determine the amount of T-Shirts that still need to be sold.

Nathan needs to sell 37 T-Shirts to get a bonus.

Let me know if you have any further questions!
@MythicalPanda