There are a number of ways the digits $2, 5, 7, 8$ can be placed in a subtraction sum like the one below:
In this example, the answer is 29.
Can you rearrange the four digits to find all the (positive) answers it is possible to make?
Here are two follow-up questions you might like to consider:
With thanks to Don Steward, whose ideas formed the basis of this problem.