Write the main product of the given reactions:
$(1)$ $C_6H_5CH = CH_2 \xrightarrow{HBr}$
$(2)$ $C_4H_{10} \xrightarrow{\text{air}, \Delta}$

(N/A) $(1)$ The reaction of styrene $(C_6H_5CH = CH_2)$ with $HBr$ follows Markovnikov's rule,where the electrophile $H $ adds to the carbon with more hydrogen atoms,and the nucleophile $Br^-$ adds to the more substituted carbon,forming $1$-bromo-$1$-phenylethane $(C_6H_5CH(Br)CH_3)$.
$(2)$ The combustion of butane $(C_4H_{10})$ in the presence of air (oxygen) and heat $(\Delta)$ results in complete oxidation to carbon dioxide and water:
$C_4H_{10} \frac{13}{2}O_2 \xrightarrow{\Delta} 4CO_2(g) 5H_2O(g)$