Which of the following is NOT a way to identify a mineral

Color, however, is the least useful property for mineral identification. One reason is that many minerals have similar colors. Also, impurities can turn colorless minerals into colored minerals.

Explanation:

if they have a finite resultant

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