Final x position: 25m cos(50degrees) = 16.06969...m

Let \(\displaystyle{v}_{{{1}\xi}}\) be initial velocity, \(\displaystyle{v}_{{{x}{f}}}\) be velocity immediately after collision, and \(\displaystyle{v}_{{{x}{3}}}\) be resting velocity.

\(\displaystyle{{v}_{{{x}{3}}}^{{2}}}={\left({0}\frac{{m}}{{s}}\right)}^{{2}}={{v}_{{{x}{f}}}^{{2}}}+{2}\cdot{a}?{x}={{v}_{{{x}{f}}}^{{2}}}+{2}{\left({0.4}\cdot-{9.8}\frac{{m}}{{s}^{{2}}}\right)}{16.06969}\) m

\(\displaystyle{v}_{{{x}{f}}}={11.22}\) m/s

\(\displaystyle{m}_{{1}}{v}_{{{1}\xi}}+{m}_{{2}}{v}_{{{2}\xi}}={\left({m}_{1}+{m}_{2}\right)}{v}_{{{x}{f}}}\)

\(\displaystyle{\left({750}{k}{g}\right)}{v}_{{{1}\xi}}+{1200}{k}{g{{\left({0}\frac{{m}}{{s}}\right)}}}={\left({750}{k}{g}+{1200}{k}{g}\right)}{\left({11.2}\frac{{m}}{{s}}\right)}\)

\(\displaystyle{v}_{{{1}\xi}}={29.2}\frac{{m}}{{s}}\)

I may be wrong though