The best way to go about this questions is to write out a formula in which x represents the original price of the dress: x*0.90=27. To see where the 0.90 came from, if Kate's dress was 10% off, she must have paid 90% of the original price (100%-10%=90%). Then, to convert a percentage to a decimal, move the decimal point twice to the left so 90% becomes 0.90. Then, our formula essentially means that 90% of some number (x) is equal to 27. To solve for x, divide both sides of the formula by 0.90 to get x=$30 which is the final answer.
