The $25.10 is 108% of the sale price.
$25.10 = 1.08n divide both sides by 1.08 = $23.24
To find the original price we must say that the sale price is 80% of the original price.
So we can write $23.24 = 80% of n or $23.24 = .8n Dividing both side by .8 we get $29.05.
So how can we do both of these in one equation? Here is one way.
($25.10/ 1.08) = .8n (I wrote it as two equation above since it explains it better)
There are other equations that will work too.
