It is very bad practice to write "Y- 25%". In order to add or subtract a percentage from a number, it must be a percentage of something! The "25%" here is 25% of what? Denis assumed you mean 25% of Y, probably because Y is the only number given. Y- 25%Y= Y- 0.25Y= (1- 0.25)Y= 0.75Y. He also then assumed you are adding back 5% of that new number: 5% of 0.75y. Is that what you intended?
What was the original statement of the original problem? Surely, it was NOT "solve Y- 25%+ 5%= 1000" because, as I explained above, that is meaningless. I suspect that the original problem was something like "A good is on sale at 25% off but there is a 5% tax added to the sale price. If you paid 1000 (dollars or pounds or francs or rupees or zlotnys) what was the original non-sale price?"
If the original price was Y then the sale price is Y- 0.25Y= 0.75Y. Then you add back 5% of that 0.75Y+ 0.05(0.75Y)= 0.75Y+ 0.0375Y= 0.7875Y= 1000. Y= 1000/0.7875= 1269.84.
