Since there are more than 6 people at the table, we know that the 18% gratuity is going to be charged. In order to multiply a number by a percent, you need to first convert it to a decimal and 18% as a decimal is .18. Just the gratuity would be .18p, but, this is where they're trying to trick you. It is asking for the total cost of the meal including gratuity. The whole meal is 100%, so you add 100%to 18% and get 118%. 118% converted to a decimal is 1.18, so the total cost of the meal including gratuity can be expressed by 1.18p.
