To solve the equation
\[ t^2 - 81 = -45, \]
first, we add 81 to both sides:
\[ t^2 = -45 + 81. \]
Calculating the right side gives:
\[ t^2 = 36. \]
Next, we take the square root of both sides. Remember that taking the square root of a number can result in both a positive and a negative solution:
\[ t = \sqrt{36} \quad \text{or} \quad t = -\sqrt{36}. \]
Calculating the square root, we get:
\[ t = 6 \quad \text{or} \quad t = -6. \]
Thus, the final solutions are:
\[ t = 6 \quad \text{or} \quad t = -6. \]