Answer
$2.75$ dollars
Work Step by Step
$y=\lfloor x\rfloor$ is greatest integer function that considers input values as greatest integer less than or equal to $x$.
Since $x=5.5$, input value becomes $5$ (greatest integer below $5.5$).
Hence, the cost will be:
$$y=0.40\cdot \lfloor 5.5\rfloor+0.75$$
$$y=0.40\cdot 5+0.75=2.75$$
