Question 20079
we use the formula

let x be the regular price.


now we know that off be discount in this case it is 20% discount.

so 

we also know that regular price - regular*0.20=12590

let regular price be x (x has 1 ahead of it)

so x-x*0.20x=12590

that is 1x-0.020x in other words

so 0.80x=12590
x=15737.5

so regular price is 15737.5

is that what the answer in your textbook say.

regular price - regular*0.20=12590

you can substitue the answr as x and check it.