This uses float: right with text-align: right.
(a) What ... (12)
(b) What ... (13)
25
This uses float: right with text-align: left.
(a) What ... (12)
(b) What ... (13)
25
The horizontal rule should overlap with the float in the same way that other borders have done - it should 'underlap' the float, being visible where it overlaps it but placed below content of the float (the borders and content of the float should be on top of it, so it shouldn't be visible where these are. In Mozilla, notice that the HR element passes OVER the DIV element, including the borders for the DIV element.