Find all the second partial derivatives.

a. ∂²t/∂r² = 36e⁻⁶ʳcos()
b. ∂²t/∂r∂() = 6e⁻⁶ʳsin()
c. ∂²t/∂()² = -e⁻⁶ʳcos()
d. ∂²t/∂()∂r = -6e⁻⁶ʳsin()