Answer :

=d/dx((t^4-6)^3) * (t^3+6)^4 + d/dx((t^3+6)^4) * (t^4-6)^3
=3*(t^4-6)^2 * (t^3+6)^4 * d/dx(t^4-6) + 4*(t^3+6)^3 * (t^4-6)^3 * d/dx(t^3+6)
=3*(t^4-6)^2 * (t^3+6)^4 * 4t^3 + 4*(t^3+6)^3 * (t^4-6)^3 * 3t^2
Simplify that if youd like