Yes your answer is correct
If interest is 5 percent then you add 5 for every 100 so
6x5=30
then you add 30 to 600 so your answer is 630
A is the mid point ==> AL = AB = 2AB
6x-17=2(2x+3) => 6x -17 = 4x +6 => 2x = 23 =>x=23/2
then just plug x into LB and AB