2. As a wave moved from one medium to another, there was a change in the
wave's speed. If the frequency of the
wave does not change, what property of
the wave must change, causing the
change in speed?

that is a hard problem I had the same one.

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