In the case of an unsymmetrical ether, the alkyl halide is always formed from the smaller alkyl group. This happens because the I− ion being larger in sizc approaches the smaller alkyl group to avoid steric hindrance. 
Caution HI is an acid and when it is hot and concentrated it means we are having an excess of HI. Iodide ion produced from HI in this reaction will act as a nucleophile.