Answer
(a) $A\times B = 17$ (out of the page)
(b) $C\times D = 0$
Work Step by Step
We can use the right-hand rule to determine if the cross-product is into the page or out of the page.
(a) $A\times B = A~B~sin(\theta)$
$A\times B = (6)(4)~sin(135^{\circ})$
$A\times B = 17$ (out of the page)
(b) $C\times D = C~D~sin(\theta)$
$C\times D = (6)(4)~sin(180^{\circ})$
$C\times D = 0$
