Structures and IUPAC names of some hydrocarbons are given below. Explain why the names given in the parentheses are incorrect.
(a) `underset("2, 5,6-Trimethyloctane (and not 3,4,7-Trimethyloctane)")(CH_(3) - underset(underset(CH_(3))(|))(CH)- CH_(2) - CH_(2) - underset(underset(CH_(3))(|))(CH)-underset(underset(CH_(3))(|))(CH)-CH_(2) - CH_(3))`
(b) `underset("3-Ethyl-5-methylheptane (and not 5-Ethyl-3-methylheptane)")(CH_(3) - CH_(2) - underset(underset(CH_(2)CH_(3))(|))(CH)- CH_(2) - underset(underset(CH_(3))(|))(CH)- CH_(2) - CH_(3))`

Explanation

(a) Lowest locant number, 2, 5, 6 is lower than 3, 5, 7
(b) Substituents are in equivalent position, lower number is given to the one that comes first in the name according to alphabetical order