Answer
H; $4.25$ miles
Work Step by Step
$30$ minutes $=0.5$ hours
$15$ minutes $=0.25$ hours
$5.5$ miles per hour $\times$ $0.5$ hours $=2.75$ miles
$6$ miles per hour $\times$ $0.25$ hours $=1.5$ miles
$2.75$ miles $+$ $1.5$ miles $=$ $4.25$ miles