Op-Amp Circuit add/subtract voltages
Your question doesn't state that you are only allowed use one op-amp. If you are allowed use two then use two inverting summing amplifiers. Use the first to sum all the positive voltages and the second to sum the inversion of those and the negative voltages.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Two stage inverting summer.


OA1 sums U\$_1\$ and 2U\$_2\$ voltages but inverts the output giving -U\$_1\$ - 2U\$_2\$.
OA2 sums (-U\$_1\$ - 2U\$_2\$) with +U\$_3\$ to give U\$_1\$ + 2U\$_2\$ - 2U\$_3\$.


It looks like homework and you seem well able to do the calculations. If you want to post your results as an answer we can check it.