so I think this is right...

cos (theta) = dot product of vectors / product of the magnitude of the vectors

you want to write the vectors like: u = 0i + 9j and v = -2i + 0j

(i know it looks redundant)

so, magnitude is easy: for u, sq rt (0^2 + 9^2) = 9

for v, sq rt(-2^2 + 0^2) = 2

and the denominator will be 9*2 = 18

dot product takes the coefficients of i and multiplies them, then adds then to the product of the coefficients of v (sounds harder than it is)

(0*-2) + (9*0) = 0

so, cos(theta) = 0/18

therefore, cos(theta) = 0

and the cos = 0 at 90 degrees (if you know the unit circle, awesome! if not, calculator works too)

so you've got a 90 degree angle between these two vectors

hope this helps!