Adiotional: No me salen 7.17* - A plave flies to the West at 600km/h for 3 hours and then to the North with the same speed, for two 2 hours. It´s average speed vector, in a coordinate system (as sthe one shown below) is: 

î and ĵ are vectors of modulus 1, also called "Versors", their objetive is to join the vectorial characteristics of a number and tell where it is pointing to. Usually it is portrayed with a little hat or a little comma above (replacing the typical i and j) . Versor î has the same direcction and sense in the x axis, as the ĵ versor in the y axis.

This beautifull problem caused a real havoc. An exam was taken and only the 17,4% of the students (deducting the 1/6 that just guessed). Almost all the students tried to solve it in a swipe, with a sigle calculation, with a formula (what a shamefull concept about physics), and very few -a 17,4% - took the job of assembling graphs and schemes. Let´s begin there.

And it´s equal to  Δr_t = 2.163 km, but to travel through it, it took 5 hours. This way, if we wanted to find the modulus of the averages speed´s total vector, the one in light blue, we should have to divide the total displacement by the total time interval.

v_mt = Δr_t / Δt_t

v_mt = 2.163 km / 5 h

v_mt = 433 km/h

But this problem does not offer us this value as a possible answer. The total average speed vector is expressed in function of it´s orthogonal components, we could call them v_mtx y v_mty.

A less ``piggy´´ way to find the answer is to search wich of the offered pairs in the answers, match with the Pitagorical sum (it´s vectorial sum), that is v_mt = 433 km/h. And there is only one. But there are other more honorable methods.

The total average speed in the X direction, v_mtx, is goint to be equal to: