-(72) = -49

Natural numbers = {1,2,3,4,...}

Whole numbers = {0,1,2,3,4,...}

0 is the only whole number that isn't a natural number.

Integers {...,-3,-2,-1,0,1,2,3,...}

Rational numbers are number that can be written as fractions
with an integer in the numerator and the denominator.  So
integers are rational numbers because they can have a 1 
denominator place underneath them.

Edwin