dx/dt=3at² dy/dt=2bt

dy/dx=2b/3at

d²y/dx²=-2b/3at²*dt/dx=-2b/3at²*1/3at²=-2b/9a²t⁴

d³y/dx³=8b/9a²t⁵*dt/dx=8b/9a²t^5*1/3at²=8b/27a³t⁷ans

though u say its a⁷t²