0.3x +y = 7 represents a linear function

Tim's phone service charges $26.39 plus an additional $0.21 for each text message sent per month. if tim's phone bill was $31.64, which equation could be used to find how many text messages, x, tim sent last month?

An investment decreases in value by 30% in the first year and decreases by 40% in the second year. what is the percent decrease in percentage in the investment after two years

What is the 9th term in the geometric sequence described by this explicit formula? an=-6. (2)(n-1) apex