5 and 15 are the first two terms in a geometric sequence. What is the arithmetic difference between the 9th term and the 7th term?	Options.
A) 3*5^2  B) 5* 3^13 - 5 * 3^11  C) 40 * 3^7  D) 40 * 3^10  E) 3^12 - 3^10
Common ratio = 15/5= 
<gadget id="calculator">15/5</gadget>
<output>3</output>
3   7th term= 5*3^7   9th term = 5*3^9   Difference = 5 * (3^9 - 3^7)   = 5 * 3^7 *(3^2 - 1)   = 5 * 3^7 * 8   = 40 * 3^7....   40 * 3^7
<result>C</result>
5 and 15 are the first two terms in a geometric sequence. What is the arithmetic difference between the 9th term and the 7th term?