Solution: Solve $2x = 60^\circ, 120^\circ, 420^\circ, 480^\circ$ within $0^\circ \leq 2x \leq 720^\circ$. Thus, $x = 30^\circ, 60^\circ, 210^\circ, 240^\circ$. Sum: $30 + 60 + 210 + 240 = 540^\circ$. - go-checkin.com