In Austin, the use of landlines has been declining at a rate of 20% every year. There are 51,000 landlines this year. Which function can be used to determine the number of landlines after x years? A f(x)= 51,000 (0.8)* B f(x) = 51,000 (0.2)* == C f(x) = 20(51,000)* D f(x)=51,000(1.2)*