It would help if you had answered the two questions I asked you (or at leats the first question).
Q1 By definition: and you can go to a calculator and evaluate. Alternatively, if you've been taught about geometric series, you can use the usual formula to evaluate it (a = 3, r = 3, n = 7).
The other two are left for you to attempt. Please show what you have done. Say where you are stuck.