Let u = < 6, -9> , v = < 1, -4> . find u - v. a) < 5, -5> b) < 10, -10> c) < 15, 5> d) < 7, -13>

To subtract vectors, subtract the x coordinates together. Do the same for the y coordinates as well.

In terms of a formula if we had the vectors u and v such that
u = <a,b>
v = <c,d>
then 
u - v = <a-c, b-d>

Let's use that to get...
u - v = <6,-9> - <1,-4>
u - v = <6-1,-9-(-4)>
u - v = <6-1,-9+4>
u - v = <5,-5>

A) <5,-5>