$\begin{align}  & m=\frac{{{y}_{2}}-{{y}_{1}}}{{{x}_{2}}-{{x}_{1}}}given\text{ }m=\tfrac{2}{3} \\ & ({{x}_{1}},{{y}_{1}})=(-1,p),\text{  }({{x}_{2}},{{y}_{2}})=(p,4) \\ & \frac{2}{3}=\frac{4-p}{p+1} \\ & 2(p+1)=3(4-p) \\ & 2p+2=12-3p \\ & 5p=10 \\ & p=2 \\\end{align}$