I want to design amplifier that do the following summation
$$V_o = 2V_1 +3V_2 +5V_3 $$
the difficult arose when design with one op-amp and all voltages are referenced to the ground .
I tried with making non inverting amplifier with gain = 7 (any gain more than 5), then putting three resistor in the non inverting input (R1 for \$V_1\$ and R2 for \$V_2\$ and R3 for \$V_3\$) making superposition three times i have three equation.
But i can't solve them; it's very difficult for me. Does anyone have an idea?