Selection of parent carbon chain for IUPAC naming
When assigning numbers to carbon atoms in an aliphatic skeleton, your first priority must be the longest carbon chain. The chain with red numbers is one carbon atom smaller than the one with blue numbers. Blue - 9, red - 8.
It's also helpful to know that when you have two carbon chains of the same length, the one that's the most branched must be assigned the highest priority. Here we have exactly this case, where two chains of the same length can be found. One of them has 4 branches (2 ethyl radicals, 1 alcohol and 1 bromide) and the other one has 3 branches (1 hydroxyl, 1 ethyl and 1-(1-bromoethyl)).