Answer
$${156^ \circ }$$
Work Step by Step
$$\eqalign{
& \frac{{13\pi }}{{15}} \cr
& {\text{we know that 1 radian}} = \left( {\frac{{{{180}^ \circ }}}{\pi }} \right){\text{. }}\left( {{\text{see}}\,\,{\text{page 668}}} \right){\text{ Then}}{\text{,}} \cr
& \frac{{13\pi }}{{15}}{\text{radians}} = \frac{{13\pi }}{{15}}\left( {\frac{{{{180}^ \circ }}}{\pi }} \right) \cr
& {\text{multiplying}} \cr
& \frac{{13\pi }}{{15}}{\text{radians}} = 13\pi \left( {{{12}^ \circ }} \right) \cr
& \frac{{13\pi }}{{15}}{\text{radians}} = {156^ \circ } \cr} $$
