Basically, we're trying to find the distance between (1, 0) (0, 0) x the distance between (2, 1) (0, 0) x the distance between (3, 0) (0, 0) x the distance between (0, 1) (0, 0)
By using the distance formula, we can find
distance between (1, 0) (0, 0) = 1
distance between (2, 1) (0, 0) = √3
distance between (3, 0) (0, 0) = √5
distance between (0, 1) (0, 0) = 1
$|1| |2i| |3| |i|$ = 1 x √3 x √5 x 1 = √3 x √5 = √15