Chapter 11 - Section 11.2 - Arithmetic and Geometric Sequences - Exercise Set - Page 647: 66

multiple answers; see details below

With $a_1= \$26.8 $ and $r= 2.5 $, then, \begin{array}{l} a_2=a_1(r)\\ a_2=26.8(2.5)\\ a_2=67 ,\\\\ a_3=a_2(r)\\ a_3=67(2.5)\\ a_3=167.5 ,\\\\ a_4=a_3(r)\\ a_4=167.5(2.5)\\ a_4=418.75 .\end{array}