Answer
(a) 40 ft-lb
(b) 12 ft-lb
Work Step by Step
(a) Arm: $i+2j$ ft
Force: $20 i$ lb
$A \times F =-40 k$
$|A \times F|= $|$i+2j$||$20 i$|$=40 ft-lb$
(b) Arm: $0.6i+0.6j$ ft
Force: $20 i$ lb
$A \times F =-12 k$
$|A \times F|= $|$i+2j$||$20 i$|$=12 ft-lb$