$\text{Let } a = 3.6$ Compute the following:

$\lceil -1.8 a\rceil =$
$\lceil a + 0.4\rceil =$
$\lceil a\rceil + \lceil -1.9\rceil =$
$\lceil 1.8\rceil -\lceil a + 2.8\rceil =$