Jon has to choose which variable to solve for in order to be able to do the problem below in the most efficient manner. 6 x 3 y = 27. 5 x 2 y = 21. Which variable should he choose so that he can use substitution to solve the system? Jon should solve for y in the first equation because the coefficients can be reduced by a common factor to eliminate the coefficient for y. Jon should solve for x in the first equation because the coefficients can be reduced by a common factor to eliminate the coefficient for x. Jon should solve for y in the second equation because the coefficients can be reduced by a common factor to eliminate the coefficient for y. Jon should solve for x in the second equation because the coefficients can be reduced by a common factor to eliminate the coefficient for x.