You need LCD or the least common denominator. For 4 over 8 and 2 over 8 have the same denominators except for 2 over 4. You need to ask yourself what times 4 equals to 8? 4 times 2 equals to 8, so multiply 4x2 for the denominator and for the numerator multiply 2x2. Whatever you do to the denominator you have to do the same thing to the numerator. You multiplied 4x2 for the denominator and 2x2 for the numerator and now your fraction is 4 over 8. Now add 4 over 8+ 4 over 8 which is 8 over 8 or 1. Now add 1+ 2 over 8 which is 1 2/8. If you simplify 1 2/8 it will become 1 1/4.
Each term is half of the previous one, so the common ratio is 1/2. Then to get from the first term to the nth term, you have to take n - 1 steps, multiplying by 1/2 each time and by 6000 to account for the first term.
