0.03x=0.30x+35; 0=0.27x+35, x=-35/0.27, x=-129.63. This is the only value for x and it's negative; y=-3.89 approx.
Check your equations for the phone plans. If x is the number of call-minutes, and 0.03 and 0.30 are the charges, it seems a bit excessive at 0.30!