$${\begin{align*} J_x &= m(v_{fx} - v_{ix}) \\&= \mathrm{(80 \, kg) [(50 \, m/s) \cos (-10^\circ) - (70\, m/s) \cos 30^\circ]} \\&= -910\, \mathrm{kg \cdot m/s}\end{align*}}$$