The three vectors have magnitude a =3m, b= 4m and c=10m . On the x axis is vector a at 0 degrees then 30 degrees is vector b then 120 degrees is vector c. If vector c =p*vector a + q*vector b .What are the values of p? and q?

I am expose to get -6.67 for p and then 4.33 for q. I don't know what i am doing wrong.

Let me see your work on a, b, c on converting them to s,y coordinates as in
a= something x + something y.

I suspect that is your error.