=  + (20-1)*d


26  =   + 19*(-5)

26 - 19*(-5) = 

26 + 95 = 

 = 121.  <<<---===  the 1-st term



 =  + (15-1)*(-5)

 = 121 + 14*(-5) = 121 - 70 = 51.   <<<---===  .


ANSWER.  1-st term is 121.   15-th therm is  51.

 1st term: 121

15th term: 51 

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