Can someone help me with this math question please!?

5500 dollars is placed in an account with an annual interest rate of 6.5%. to the nearest tenth of a year, how long will it take for the account value to reach 19700 dollars?

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Which of the expressions (on the photo document i inserted) together represent all solutions to the following equation? 8cos(12x)+4=-4 *the answer should be in degrees.* > i would like for someone to explain the process to find the solutions for this.