Question

T3=-6.5 and t5=-3.9 determine d

Answer 1

$t_3=-6.5;\ t_5=-3.9\\\\t_5-t_3=2d\\\\2d=-3.9-(-6.5)\\\\2d=-3.9+6.5\\\\2d=2.6\ \ \ \ |divide\ both\ sides\ by\ 2\\\\\boxed{d=1.3}$