We have $64=2^6.$ Hence
$3^2=9\\
3^4=9^2=81\equiv 14\; \mod \; (67)\\
3^8\equiv14^2=196\equiv62\equiv -5 \; \mod \; (67)\\
3^{16}\equiv (-5)^2=25\; \mod \;(67)\\
3^{32} \equiv 25^2 =625 \equiv 22 \; \mod \; (67)\\
3^{64}\equiv 22^2 = 484 \equiv 15 \; \mod \; (67)$