Let c represent the original amount that this guy had saved up.
He spent 25% of this amount, or 0.25c, on the printer.
To progress further, we have to know how much the printer cost.
Supposing that the printer cost $100 (which we do not know as a fact), this would be equal to 0.25c.
Thus, his savings originally amounted to c = $100/0.25 = $400.
