Answer
$${54^ \circ }$$
Work Step by Step
$$\eqalign{
& \frac{{3\pi }}{{10}} \cr
& {\text{we know that 1 radian}} = \left( {\frac{{{{180}^ \circ }}}{\pi }} \right){\text{. }}\left( {{\text{see}}\,\,{\text{page 668}}} \right){\text{ Then}}{\text{,}} \cr
& \frac{{3\pi }}{{10}}{\text{radians}} = \frac{{3\pi }}{{10}}\left( {\frac{{{{180}^ \circ }}}{\pi }} \right) \cr
& {\text{multiplying}} \cr
& \frac{{3\pi }}{{10}}{\text{radians}} = \frac{{3\left( {{{180}^ \circ }} \right)}}{{10}} \cr
& \frac{{3\pi }}{{10}}{\text{radians}} = 3\left( {{{18}^ \circ }} \right) \cr
& \frac{{3\pi }}{{10}}{\text{radians}} = {54^ \circ } \cr} $$
