If you travel for three hours at a speed of 30 km/h , how far will you go?

Distance = (speed) x (time)  <== This is important.  You should memorize it.

Distance = (30 km/hr) x (3 hr)

Distance = (30 x 3) (km/hr x hr)

Distance = 90 km

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west

e/c, where e is its total energy