well, if he wants 50% lemon and 50% lime, and there's already 30% lemon and 70% lime, then he would have to add 40% more lemon juice i belive, because he wants it half and half lemon and lime
To get this you would need to subtract 7-3=4, and then add the 0's on the end, 40%, because 70% and (30% + 40%) = both to be 70%, so really it's half and half i believe
sorry if i got this wrong, i'm not very good with these things, but i hope this helped!
