solve simultaneous equation (novice)

[message]

Readers,

The function 'fsolve' was attempted to be used to solve the following 
simultaneous equations:

equation 1: 4.2=2x+4y; equation 2: 6.3=4x+y

function y=f(x)
ya=-4.2+2*x+4*4.2/4-2*x/4;
yb=-6.3+4*x+4.2/4-2*x/4;
endfunction
[x,info]=fsolve(@f,[1;2])

warning: f: some elements in list of return values are undefined
warning: f: some elements in list of return values are undefined
warning: f: some elements in list of return values are undefined
warning: f: some elements in list of return values are undefined
warning: f: some elements in list of return values are undefined
warning: f: some elements in list of return values are undefined
x =

   1
   2

info = [](0x0)

Manual solution:

Rearrangement to
4y=4.2-2x, 4.2/4-2x/4

6.3=4x+4.2/4-2x/4 -> 25.2=16x+4.2-2x -> 25.2-4.2=16x-2x -> 21=14x -> 
x=3/2

4.2=2*3/2+4y -> 4.2=3+4y -> 1.2=4y -> 1.2/4=y -> y=.3

Please what is my error in octave syntax to prevent the same result in 
octave as in the manual method described?