The first one is 31.875 and the second is 12 I don't know how to explain to get it. Sorry
Aos= -b/2a so plunin your numbers and you'll get the AOS so you can find the vertex
Answer:7043.82
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