When you're diluting a solution, you are decreasing its concentration by increasing its volume while keeping the number of moles of solute constant.
This implies that the increase in the volume of the solution must be equal to the decrease in the concentration. In other words, volume increases and concentration decreases by the same factor, the dilution factor.
In your case, the volume increases by a factor of
#(789 color(red)(cancel(color(black)("mL"))))/(234color(red)(cancel(color(black)("mL")))) = color(blue)(3.372)#
This means that the concentration will decrease by a factor of
#c_"new" = "2.34 M"/color(blue)(3.372) = color(darkgreen)(ul(color(black)("0.694 M")))#
The answer is rounded to three sig figs.