Change the MOO into SOO?

I have three objective function equation that I genereated from design of experiment. I performed the genetic algorithm optimization for solving multi-objective optimization then generated a pareto frontier best solution to look at the trade-off. However, I'd like to change the MOO into SOO to find the best solution.

y(1) = -(-4.398907104 + 69.627287709*x(1) - 73.88575606*x(2)); %NPV

y(2) = 5.5828360656 + 0.0697243039*x(1) - 0.052863409*x(2); %FEDI

y(3) = 119.81506557 + 1291.2552396*x(1) - 249.4926284*x(2); %GWP

how could I change the equation into one equation?