1/9+1/8 is 0.2361. That would honestly be closer to zero but the way that it is worded, it is closer to 1/2 because you are using fractions in the problem. If you were using decimals, I would use 0.5
It would be 4200 x 1.09 which is the interest to the power of 6 for the number of years which would then give you 4200 x 1.09^6. This will then give the answer of 7043.82