Find the exact length of the helix r(t)= 10cos(2t5), 10sin(2t5), 3t \displaystyle \vec{{r}}{\left({t}\right)}={\left\langle\ {10}{\cos{{\left(\frac{{{2}{t}}}{{5}}\right)}}},\ {10}{\sin{{\left(\frac{{{2}{t}}}{{5}}\right)}}},\ {3}{t}\ \right\rangle} for 8t6\displaystyle -{8}\le{t}\le{6}.