Answer
$|v_3| =1.2km/h$
Work Step by Step
$d=(90i) km$
$ d_1+d_2 = (60i-20j)km$
Getting the distance, $d_3$:
$d= d_1+d_2+d_3$
$d_3 = d- (d_1+d_2)$
$d_3 = [90i- (60i-20j)]km$
$d_3 = [30i +20j]km$
Getting the velocity, $v_3$ from the distance, $d_3$ and time, $t_3$:
$v_3 = \frac{d_3}{t_3}$
$v_3 = \frac{(30i +20j)km}{30h}$
$v_3 = (i + 0.667j)km/h$
$|v_3| = \sqrt {1^2 +0.667^2}$
$|v_3| =1.2km/h$
