



 
Hi, The defining feature of an arithmetic progression is that there is a number $d$ so that to get from any term to the next you add $d.$ Thus to get to the third term from the first term you add $d$ twice. What is $d?$ Does this agree with "5th term is 15 more than the second"? Suppose the first term is $a.$ Using the value of $d$ you found above, what is the 7th term? This is 7 times $a.$ What is $a?$ Penny  


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