Five different problems in one post? That's a turn-off for some potential helpers. Suggest you post only ONE problem at a time.
In regard to the first problem: Your Principal (P) is $8000. The Interest Rate (i) is 19%. The elapsed time is 7 years. Using the formula for continuous compounding:
A = P e^(rt), where "e" is the very common base with value approx. 2.718.
Here, the amount due is A = $8000 * e^(0.19 * 7). Can you evaluate this?
