Will give brainliest! Can anyone help me with part B of the question?

Find the sum of the following series. round to the nearest hundredth if necessary.

In simplified exponential notation, the expression a^2•a^-3•a 1/a 0

Tim's phone service charges $23.06 plus an additional $0.22 for each text message sent per month. if tim's phone bill was $28.56, which equation could be used to find how many text messages, x, tim sent last month?