You need to find the x-component of each of the three force vectors, then add them. So starting with 3 N acting along (-3, -2, -9): the magnitude of this directional vector is sqrt(3^2+2^2+9^2) = 9.969, and the portion acting in the x direction is -3/9.969 = -0.3094. Multiply by 3N to get -0.928N. This is the amount fo force acting in the x-direction for the 3N force. Repeat this for the other two vectors and add, and you should get Fx = -0.928N + 3.068N +2.828N = 4.968N.