a) Since a^2 will give a 0 or positive value, you choose 0 since it is smallest. choose largest number for b with negative sign, as squaring it will give biggest number (the negative sign disappears)
b) Since b is negative, you need a negative number for value of a, to make the result positive. Negative signs will cancel each other, so just choose largest number for a with negative sign and smallest number for b with negative sign