The opposite of a number is the same number but but with the opposite sign (+/-). E. G. The opposite of (+)2 is -2.
If N is less than its opposite, than it means that it is negative as its opposite will be positive (greater than 0). E.g. If N=-2, its opposite would be 2.
to find out how much pizza is needed, multiply 4/7 by 18 to get 72/7. round up to get 77/7 or 11 pizzas. 77/7 - 72/7= 5/7 so there will be 5/7 left over