Solving this math problem with a mathematical written explanation

Which of the following contains a variable?

What would be the reasons for lines 3 and 4? a. addition property; subtraction property b. addition property; solve c. substitution property; subtraction property d. substitution property; prove

Asequence has a common ratio of and f(5) = 81. which explicit formula represents the sequence? f(x) = 24 f(x) = 16 f(x) = 24 f(x) = 16