To work out how much something was before the discount, you have to divide the price (which is £90) by 75 (as this is the percentage that you paid). It's gives you £1.20. Therefore, 1% is £1.20. To find the original cost, which is 100%, you have to multiply it by 100. Multiplying £1.20 by 100 gives you £120. Therefore, the cost of the TV before the 25% reeducation was £120. Hope this helps :)