How do I solve for x?

What is the value of the expression below? (81^2)^1/8

Which of the following is missing in the explicit formula for the compound interest geometric sequence below?

Use the linear combination method to solve the system of equations. explain each step of your solution. if steps are not explained, you will not receive credit for that step. 2 + 9 = −26 −3 − 7 = 13