Once again break down the question:
All prices are reduced by 18%, so sale price is 100% (normal price) - 18% (sale price) = 82%. As we know what the sale price is, but we DO NOT KNOW the normal price we can put this into a formula: x * 0.82 = 25.83. Now tell yourself, find x. Finding x goes to : x = 25.83 / 0.82. Put into calculator to find: x = 31.5