The circulation C of a certain magazine as a function of time t is given by the following formula. 6.2 CE - 0.1 + 0.3 Here C is measured in thousands, and t is measured in years since the beginning of 2006, when the magazine was started. (a) Make the graph of C versus t covering the first 6 years of the magazine's existence. 50 50 60 40 301 20 20 10 2 O 2 3 4 5 O 60 60 50 50 40 40 30 30 20 20 10 10 4 3 5 5 2 4 O 3 6 (b) Express using functional notation the circulation of the magazine 21 months after it was started. 21/12 .Find.that.value..(Round your answer to two decimal places.) X thousand magazines Enter a number. (c) Over what time interval is the graph of C concave up? The graph of C is concave up from t = 0 (smaller value) to t = X (larger value) years